INSTRUCTIONSFOR

USEAND

ADJUSTMENTOF

GEODETICLEVELSS500 SERIES

LTD

S500.

A Trivet stage.

H ravelling screws.

I Adjusting caps for level-ling screws.

L ' Sprung plate securinglevelling screws to tri-brach.

1-) Circular spirit level.

H Main spirit level.

K Guard protecting prismreading device.

(1 Reflector for main spiritlevel.

INSTRUCTIONS FOR USE

Levelling Procedure. In us ing these instruments t h - 1

Surveyor may i:lect to record two readings at each sight (OIK:with level on left of telescope, the other with level on right iin which case the mean will be the true reading, and the relationship of the spirit level to the telescope may be ignored. Whenfollowing this procedure, however, it is essential that the imagesof the two lines engraved on the level vial shall be coincidentwhen viewed through the reading system (see note under fig. 3)

It it is intended to book only one reading at each sight,which incidentally should always be done with the level on theleft of the telescope, the relationship of the spirit level to thetelescope line of sight should be periodically checked. Theprocedure is described in paragraph 8, page 13.

Levelling operations may be carried out by any of thelollowing methods :—

(a) By levelling the telescope precisely and estimatingthe staff fractions.

(b) As (a) but determining the fractions by use of theOptical Micrometer (see page 9).

(c) By directing the telescope cross wires to the star!division nearest to true level and recording the positionof the bubble (fig. 3) and the stadia intercept fromwhich the true reading is later computed.

(rf) By levelling the telescope approximately and recordingthe position of the bubble, the stadia intercept andthe staff division fractions given by the OpticalMicrometer.

Methods (a) and (b) involve the process of levelling thetelescope precisely but give direct results in the field. It isopen to the observer to check the relationship of the spirit levelto the telescope before commencing operations and thereafterto rely on one reading per sight with the level on the left sideof the telescope, or to disregard this relationship and to book"face right" and "face left" observations throughout.

Methods u,j ,tml ( ( / [ < i \ o i < l ,ni rM i m ; i t i > ' • . ; ot stall divisiontractions at the cost of some computational ">vork and greatlyspeed uj) the field work. Method Vi is the system used by theHritish Ordnance Survey Office \\'hen employing the bubblescale, observations must be taken with the bubble on the leftside only, since the bubble scale constant holds good only onthis lace. The reason for this is that the optical conditions arenot the same with the vial erect and inverted since in the lattercase the fluid is interposed between the air space and the bubblereading system. The magnification is therefore less whenreading with the bubble to the right and inverted, and thevalue of an interval of the scale division is therefore increased.

When using methods ( r ) and fill therefore the relationshipof spirit level and telescope should be checked and correctedbefore work is commenced. See paragraph 8.

In order to eliminate as far as possible both personal andinstrumental errors it is desirable to observe the followingprocedure :—,

1. That back and fore sights should be equidistant.

'2. That two staves be used and that at positions whereno bench mark exists a staff plate be employedto ensure that no error is introduced in reversingthe staff.

3. That the whole section should be relevelled in theopposite direction with the position of the stavesreversed, i.e., if the first traverse terminates withstaff 15 the return traverse should commence withstaff A.

Klimination of Parallax.

(a) Commence with the eyepiece screwed right out andscrew inwards unti l the cross lines on the graticule are sharplyfocused. To facilitate this adjustment it may be found con-venient first to put the telescope out of focus so that thecross lines only are seen in the field of view.

(b) Point the telescope at the staff and focus by turningthe knurled head on the side of the telescope until the object issharply defined.

The image of the object and the crosslines shouldnow be in the same plane, so that when the eye ismoved up and down no movement of the imagerelative to the crosslines (i.e., parallax) is apparent.

Presence of parallax indicates incorrect focus.

Hubble Si-ale.T i n - S5MII I . e v i l has .1 scale m t < - i -posed w i t h i n j . ln- b u l > t . ! <

reading svstcni, the purpose oi w h h h is to avoid tile necessity !orlevelling tin- telescope precisely. Tin1 departure irotn true IKVI-!is indicated l i v t h i s -.ualu and a r o r r o p ' i i u l i i i K allowanci ' nuidilo the stall reading. \^':(-' fit^. 3' .

1-ig. 3I'ield of view of telescope eyepiece.

rheUre appearing iu both halve-, ttf the coincidence svstetn (iniiiK-iliately undertlit-divisjou numbered 0) represents the two index marks on the spirit level, sop para, s

1. Method of using Bubble Scale.In order to determine the correction to true level, it i-

necessary to know:- —(a) The angular value represented by the bubble

divisions.(b) The number of divisions of bubble scale separating the

bubble end images.(c) The distance of the start as indicated by the stadia

intercept.

COTTON 1-OK kt'.N Ol UUBBU: l\N THOUSANDTHS Ol A I-'OOT.1 BUBBLE DIVISION" « 1.00 sec.

Divisionsbetweenbubbleimages

0.5 — 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6 7 7 7 7 8 8 8 -.

1.0 1 1 2 2 3 3 4 4 5 5 K 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 I K 16 M-

1.5 I 2 3 4 4 5 K 7 7 S 9 9 Kl II 12 12 13 14 14 15 16 17 17 IS 19 20 20 21 22 22 23 24 25

2.0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15 16 17 IS 19 20 21 22 23 24 25 26 27 28 29 3o 31 32 ,u

2.5 2 4 5 6 7 8 1(1 11 12 13 15 IS 17 IS 19 21 22 23 24 25 27 28 29 30 31 33 34 35 36 37 39 4n 4i

3 4 6 7 9 10 12 13 15 I f i 17 19 20 22 23 25 26 28 29 30 32 33 .35 3fi 38 39 41 42 43 4 5 46 is •!:•

3 5 7 8 10 12 14 15 17 19 211 22 24 25 27 29 30 32 34 35 37 39 41 42 14 -IB 47 49 51 52 54 56 >•,

4 6 8 10 12 I I 16 17 19 21 23 25 27 29 31 33 3.5 37 39 41 43 45 47 49 5n 52 .54 53 58 60 (12 61 «>•

4 6 9 I I 13 1.5 17 20 22 2 1 26 28 31 33 35 37 39 41 44 4K 48 50 52 54 57 .59 61 63 65 68 70 7'.' li

5 7 I I I 12 15 17 19 22 21 27 2.1 31 31 3(i 39 41 44 46 48 51 53 5K 58 fid K3 65 6.8 7O 73 75 77 so s.'

5 S I I 13 I K 19 21 24 27 29 32 35 37 4O 13 45 48 51 53 56 59 61 64 67 69 72 75 77 80 8,1 N.S SN 91

6 9 12 15 17 '20 23 26 29 32 35 38 41 44 47 49 ,52 55 58 Kl 64 67 70 73 7(i 79 81 84 87 9o 93 9" 9."

6 9 13 Hi 19 22 2.5 28 32 35 38 41 44 47 50 54 57 60 R3 6B 69 72 76 79 82 85 88 91 95 98 101 104 107

7 10 14 17 20 24 27 30 31 37 41 41 47 51 54 58 61 64 68 71 74 78 SI 85 88 91 95 9,8 101 1O5 108 112 l|5

.20 .30 .40 .SO .BO .70 ,80.90 1.0 1 1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 0 2.1 2.2 2.3 2 4 2.5 2.6 2.7 2 8 2.9 3.0 3.1 3.2 3 3 3 4

STADIA ( I - E K T l

The adjoining table is constructed on the assumption thatone division difference on the bubble scale corresponds to 1second of arc. It is not possible to produce instruments all tohave a uniform value to within 1;10th of a second, but theactual constant is supplied with each instrument and it isnecessary to multiply the correction obtained from the tableby this.

The left-hand vertical column of the table represents divisionsbetween bubble images and the bottom horizontal column thestadia reading in feet. The corrections are given in tenthousandths of a foot.

Thus, if the separation of the bubble images is 2.5 divisionsand stadia reading 1.1 ft. the correction taken from the table is.0013 ft. If the bubble scale is 1.3 seconds per division, thecorrection is 0.0013 x 1.3 = 0.0017 ft.

Fractions of bubble scale and stadia readings can, of course,be dealt with by interpolation.

With regard to the sign of the correction, if the left-handbubble image is-uppermost the telescope is depressed and thereforethe correction must be added to the observed staff reading, whilstif the right-hand image is uppermost the correction must besubtracted.

2. To ascertain the bubble constant.

1. Set up instrument and staff on level ground about300 feet apart.

2. Direct telescope (with spirit level on left, see page 2)on to staff and set the right side bubble image near oneextremity of its run, note bubble scale reading (a) (righthand image in relation to scale) and staff reading (x).

3. Tilt telescope till right side image nearly reachesother extremity of run, again note position in relation [to scale(6) and staff reading (y).

4. Observe distance of staff (in feet) as indicated bystadia lines (S).

5. Solve x—y

S x (a — b)

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6. Apply result to Circular Measure of angles table(length of arcs to radius — 1) from which is deduced theangular value of one division interval between bubble images,i.e., bubble constant.

7. The result may be obtained without the use of tablesby multiplying the figure obtained in (5) above by 206265.

3. Special Attachment for Reading to 0.001 ft.

Fig. 4.

The micrometer attachment shown in section above con-sists of a parallel glass plate, placed in front of the object glassof the telescope, and mounted so that it may be tilted by meansof a micrometer head divided into 20 divisions and situated atthe eye-end of the telescope. The attachment which is packedseparately in the instrument box may be fitted or detachedin a few seconds.

When the glass plate is vertical, of course, the direction of therays of light from the staff is not affected, and the horizontal cross-line of the diaphragm intersects the same level on the staffas when the attachment is not in use. If the glass plate beinclined to the vertical, the direction of the rays of light from Hiestaff is slightly displaced by refraction, with the result that thehorizontal cross-line may be brought to coincide with thenearest staff division. The amount of the displacement is readfrom a graduated pinion which carries twenty divisions cor-responding to a total displacement of 0.02 of a foot. Henceone division on the micrometer head represents a vertical intervalon the staff of 0.001 of a foot, irrespective of distance.

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i i i ) Instructions for use with staff divided to 0.02 ftTin- t ra i l ional addendum is made always of -one sign hv

t i iHowing the procedure adopted by the British OrdnanceSurvey Oitice, and in this case the micrometer head is engravedn 2U. Id being the reading when the glass plate is vertical.

At the outset the parallel glass plate is inclined as far as itwill go, unt i l the drum reads 0. The initial image shift introducedby this procedure is of no importance since it obviously cancelsitself out when levels are transferred. In the example given infig. 5 the reading, 5,84 ft., is obtained^ direct through thetelescope, whilst the addendum (0.005 ft .) is obtainetl bytraversing the middle horizontal line of the diaphragm back tothe last division on the staff (by the micrometer drum), in thiscase 5 divisions.

.— INVAR STRIP DIVIDEDTO O2 FT.

'Fig. 5.

Published hy permission.

(b) Instructions for use with staff divided to 0.01 ft.Using this form of staff two coincidences can be made by

traversing the middle horizontal line of the diaphragm back alongthe staff. Suppose the staff reading is 7.63 plus a fraction ofthe next hundredth of a foot. When coincidence is made betweenthis line and the horizontal wire the micrometer drum reading(say 0.006) plus this will give the true reading, 7.63 4- 0.006Additional rotation of the micrometer head will produce a secondcoincidence, this time with the 7.62 staff graduation, at whichsetting the micrometer will read 0.016, The same reading isobtained as before, viz., 7.62 + 0.016 == 7.636.

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4. Gradienter Micrometer Scales.There are two scales, viz. :

( 1 ) The Vertical Scale (V in Jig.) lor count ing the number ofcomplete turns made by the drum.

(2) Tlit Horizontal Scale (Hin fig.) for giving fractions ofone revolution.

X.B.- Kead RED figureswhen red portion of V is exposed.It will be. found convenient toconsider :—'"Red rigures and Rising Grad-ients as Plus.

Black figures and FallingGradients as Minus.

One revolution of the screwtilts the line of sight by 1 in 1000.The drum is divided into 50 and1/100 rev. can easily be read byestimation. Thus the readinginthefigure is — 1 rev. on Scale V and23/100 rev. on Scale H= - 1.23.

10 complete revs, of drum (up or down, starting from zero) =10/1000, or a grade of 1 in 100.

20 complete revs, of drum (starting from either end ofscale V) = 20/1000, or a grade of 1 in 50.

5. To measure a Grade.Drum revs.

Grad,ent= —1000-

(a) Set up the instrument (as described in section 1) onthe line of the grade and point the telescope along the same.

(//) Set the micrometer scales to zero and bring the bubbleof the long spirit level to the centre of it.-* run by means ofthe footscrews.

(c) Take "Height of Eye" of instrument by means of alevelling staff or use a target staff made so that the targetwill slide up and down and be adjustable to the Height ofF.ye (i.e., l ine of collimation.)

(rf) Erect staff on the selected spot and by means of thegradienter screw bring the middle horizontal line of diaphragmto bear on target or "Height of Eye" on staff.

I I

i c ) lake the reading of the scales, say - l . K

The gradient ™ -x.^j. — - ^ _ or a "down" grade of 1 in 625.

6. To Lay Down a Grade.

Say- a gradient of 1 in 625 is required.

1 drum revs. 1000I lien ,,„-= SXK~ therefore drum revs. = -^^~ 1.6.o^v"> ozr>

(a) Perform the instructions (a), (ft) and (c) in section 5.

(ft) Tilt the telescope the required amount by setting themicrometer screw to 1.6 (+ or — as required) and drivepegs as necessary into the ground so that when the staff i>mounted on them, the gradient line given by the level will pas?through the target or "Height of Eye."

7. Distance Measurements by Subtense Method.

This is particularly useful for distances beyond the rangeof stadia readings and for measurements across rivers andravines, or from spur to spur in difficult country.

„. n x 1000Distance = -,drum revs.

where n = number of feet on staff or between two targetstraversed by diaphragm line.

(a) Point the telescope at the staff and bring the middlehorizontal line of the diaphragm to bear on to one of twcprominent marks or targets placed a convenient distance (sa>10 ft.) apart. Take the reading of the scales.

(ft) By means of the fine-setting screw bring the diaphragrrline to bear on the second mark or target and again take thtreading of the scales.

Example :—If the difference in reading obtained by aand (f t ) = 6.28 revs.

Then distance =- = 1,592 feet.

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ADJUSTMENT INSTRUCTIONS

8. Adjustment of Main Spirit Level.

(a) Set up the instrument and tripod firmly on solidground and bring the bubble of the circular spirit level centralby manipulation of the tripod legs and the footscrews.

(//) Eliminate all traces of parallax, as instructed on page 5.

(c) Observe through the prism reader the position of thetwo lines engraved on the glass tube of the spirit level (see fig.3. page 6).

If these are not found to be coincident, release lock-nut on the prism reading device and turn milled head (H) untilthey are coincident.

(rf) With the spirit level on the right side of the telescope,focus the telescope on to a staff erected at a convenientdistance, say 100 feet.

(e) Now make the two ends of the bubble coincident byrotating the micrometer drum (J) and note the reading on thestaff of the central horizontal line in the diaphragm

(/) Rotate the telescope in its barrel through 180°, thusbringing the spirit level on the left of the telescope.

If now the ends of the bubble coincide when thereading on the staff is the same as obtained by (e),the spiritlevel and the line of collimation of the telescope are parallel ;but if not, then -

(f) Bring the ends of the bubble coincident by rotatingthe micrometer drum and note the reading on the staff.

The mean of the two staff readings (beingthe absolute level) is the datum line then re-quired for making the necessary correctionthus :—

(/() Direct the telescope to the mean of the two star}readings by rotating the micrometer drum.

(i) By means of milled head on the prism reading devicebring the two ends of the bubble coincident, ignoring the positionand any lack of coincidence of the lines engraved on the glasstube of the spirit level. Secure this adjustment by the lock-nut.

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The- ad jus tmen t is nn» i innpl i- ted. . - . , . , t i n - inn' i f rollimat ion ol the U-U--ropc is hon/ontai, u h c nwith the spirit level on the left side of the tele-scope (he two ends of t in - bubble appear coincidentin the reader. Provided these instructions have beencarefu l ly followed, the instrument will be in adjustmentto within " 1 sec. of arc.

Alter the adjustment has been completed, therelative position of the lines on the glass, tube of thespirit level is immaterial and should be ignored.

Since the, prism reader has been set with thespirit level on the LEFT of the telescope, it followsthat the instrument MUST always be usedwith the spirit level in that position.

(j) The above adjustment may also be carried out bymeans of the adjusting screws situated under the circularplate at the front end of the long spirit level. In this case theprocedure indicated under (c) to (h) is followed, but the twoends of the bubble are then made to coincide by means of thevertically oppqsed adjusting screws. It will then be necessaryto correct the adjustment for "roll" of the spirit level by rotatingthe telescope in its barrel through 90° observing whetherthe bubble alters its position with regard to the engraved lines,and correcting by means of the horizontally opposed screws.

Repeat (c) to (j) until correct.

If the adjustment is carried out in this manner the .relative position of the lines on the spirit level is altered andthe instrument may be used with the spirit level on either tin-left or right of the telescope.

9. Adjustment of Micrometer Drum.

For this adjustment it is necessary to set thevertical axis truly vertical, and this is done in thefollowing manner :—

(a) Place the telescope parallel to two of the footscrewsand by adjusting these bring the ends of the bubble coincidentin the prism reader.

(b) Rotate the telescope on its vertical axis through180°, and if the ends of the bubble depart from coincidence,halve the difference by the micrometer drum and take upthe remainder by means of the footscrews.

14

I t ) Rotate the telescope on its vertical axis through 9i>- i > that it lies directly over the other footscrew and by adjustingthis bring the bubble ends coincident.

(d) Kotatc the telescope on its vertical axis through 180-and correct any departure of the bubble ends tromi coincidence —half by the footscrew and half by the micrometer drum.

The vertical axis will now be approximatelyerect and the above procedure should be repeated untilcoincidence of the bubble ends is obtained for alldirections of the telescope without adjustment ofeither footscrews or micrometer drum. The line ofcollimation of the telescope will now be perfectlyhorizontal and the micrometer drum should read zero.

(e) To reset, if necessary, loosen the locking screw in theknurled portion of the drum and revolve the engraved portionin its sleeve,until it reads zero.

(/) Tighten locking screw.

10. Adjustment of Circular Spirit Level.

Complete the whole adjustment of the instrument bycorrecting the circular spirit level by its own adjusting screws.

In the ordinary course of work the instrument is set upapproximately level with reference to this circular spirit levelby manipulation of the tripod legs and the footscrews.

11. Adjustment of 180° Rotation of Telescope.

Adjustable stops are fitted at the eye-end of the telescopebarrel, governing the 180° rotation of the telescope therein,that is to say, ensuring that the horizontal line of the diaphragmis truly horizontal in both "bubble left" and "bubble right"positions. This is an adjustment which should not requirealteration by the user, but if necessary it is carried out as follows.

Having set the vertical axis truly horizontal as describedin para. 9, (a) to (d), direct the telescope to a well denned pointat the same height as the horizontal line of the diaphragm,and by means of the azimuth slow motion screw cause the saidpoint to travel along the line, correcting any divergence bymeans of the left-hand stop in the "bubble left" position andthe right-hand stop in the "bubble right" position.

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(I'rnfiirlnrs: VITKKRS, LTD-!

HEAD OFFICE AND INSTRUMENT FACTORYYork, England

Telegrams : "Coordinate, York"Telephone: York 4112 (3 lines)

LONDON OFFICE AND SHOWROOMSBROADWAY COURT, WESTMINSTER, LONDON*, S.W.I

Telegrams : "Coordinate, Sowest London"Telephone : Whitehall 9628 (2 lines)

BIRMINGHAM OFFICE-1 ST. PAUL'S SQUARE, BIRMINGHAM, 3

Telephone : Central 1919

MANCHESTER OFFICE163 STRETFORD ROAD, MANCHESTER, 15

OVERSEAS BRANCHES AND SERVICE DEPOTSJOHANNESBURG

21 LOVEDAY STREET, JOHANNESBURGP.O. Box 7131

Telegrams : "Coordinate, Johannesburg"Telephone: 31 .'1993

CAPE TOWNSUN BUILDING, ST. GEORGES STREET, CAPE TOWN

P.O. Box 1552Telegrams: "Coordinate, Cape Town"

Telephone : 2/2727

TORONTOROOM No. 8, 61 COLLEGE STREET, TORONTO

Telephone : Elgrin 1939

16

*" * -.,. (a) Set up the geodetic level (without parallel plato. micrometer)on solid stable ground and bring'the bubble of the circular spiritlevel iu to the centre of the etched circle. If it will notremain in this position when the instrument is rotated then thi?bubble requires adjustingo The method is as for the S400 and Li^A-lcircular bubble adjustmento

(b) Obnerve through the prism reader (seen in the field of view ofthe eyepiece) the position of the two lines engraved on the glasstube of the spirit level, if these are not coincident, releasethe locking nut on the pri:n reading device and turn the millednut at the eye end of the bubble mounting until coincidence isachieved,

(c) Rotate the telescope in its barrel through 180 so that the bubblemounting is to the right of the telesoope« (This is usually calledthe Fell, position). Focus the telescope on to a stave erected about100 feet,array*

(d) Ha1.:o the two ends of the bv.bble coincident by rotating the finelevelling or gradientsr screw and record the reading on the staveof the level hair of the diaphragms

(e) Rotate tho telescopo in it.-, barrel through 100 so that the bubblemounting ir> to the left of th.3 tel,scope, i.e. at the J?»L. position*If the ends of the nubble remain coincident and the stave readingis the sane as in (d)| the spiritj evel ana the line of collinationof the telescope are parallel anr! clc not require adjusting.

(f) If the ends of the bubble are not coincident, make them so, "ryturning the fine levelling sox-er; (or gradienter drum) and note therR'icl"jrMj '''raa .the atpvcu The rv*t<.*>. ">f th« two roaC^SS* 1>e« between(d) and (f) is then the level liiu , or the tip.tun lir.e, for correct-in, the ri' i-parali'. .Lity between tho horizontal plane of the buH'<.^ana the li.i^ of co_LLinatio>: of the telescope.

(g) To :.:ake th _-se plan-: 3 parallel, direct the level hair on to theiner.n of th.- two re.-,-lings by using the gradienter drum. This willthrow the bubble out of coincidence; bring the bubble ends backto coincidence again by means of the milled head screw on the prisnreading device. This will disturb the coincidence of the lines(300 (b) above).and may be ignored. Secure the locking nutmentioned in (b), the adjustment ia now completed: io60 theliue of ccllination of the telescope is horizontal, when, with thespirit j.ev3l_onijbh_fi .left s?de of the telescope (iee.: at PL},the two end3 of the bubble appear coincident in the reader.

(h) After completion of (b) -t.o (g) the instrument is adjusted for oneposition o*il£ of the spirit level, relative to the telescope,i0e, i hen viewing from the eyepiece towards the objective, whenthe bubble is at FL position* However the above adjustment mayalso be carried out by means of tha capstan headed adjusting screwssitxiated under the circular plate, at the front end of the longspirit levela In this case the same procedure (from (b) to (§))is followed, but the two ends of the bubble are then made tocoincide by means of the vertically opposed adjusting screwsinstead of the milled head screw. It will then be necessary tocheck the adjustment for "roll" of-the spirit level by rotatingthe telescope in its barrel through 90 > observing whether the

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bubble alters its position, with regard to the engraved linesreferred to in (b) above* Correction if necessary is by meansof the horizontally opposed screws referred to in this paragraph*,Repeat until correct for all positions of .the bubble iee. atFL, 90 & ER0

If the adjustment is carried out in this manner the relativeposition of the lines on the spirit level is altered and theinstrument way ba used with" the spirit level in either PL or FRposition, .. , ... .

For this adjustment it is necessary to set the vertical axis truly vertical,and this is done in the following manner :-

(a) Place the telescope parallel to two 01 the footscrews and byadjusting these bring the end , of the bubble coincident in theprism rea.de r»

(b) Rotate the telescope oa its vortical axis through 180 , and if theends of the bubble depr-.rt fror,, coincidence, halve the differenceby the micrometer drain and tcp:e up the remainder by means of thefootscreT7S,>

- .. •

(c) Rotate the telescope en its vertical axia through 90 so that itlies directly over tiv other f ootaor. :~z and by. adjusting this bringtha bubole ends coincident,,

(d) Rotate the telescope en its vertical a:-cis through 1cO and correctariy departure of the babble e;ids frorr. coincidence - half by thefootscrews and half .by the .micrometer druia0The vertical ruis will nc™ be approximately vettiaol and th°. &"boveproce. .ure should be repeated until coincidence of the bubble endsis obtained for all direction.- of th-i telescope vd-lhout adjustir.tncof either ~?oc screws cr micrometer drum.c The line of collinationof the telescope vail 110*7 be perfectly horizontal and ths ndcro-meter drum shculd rcacT zero.

(e) To reseltj, if necessary, loossn the locking screw in the knurledportion' of thi- dinun and revol^a the engraved portion in its sleeveuntil it reads zeros ;

(f) Tighten the locking eorsw* "•: ••

3» Adjustment of circular _ spirit level : .

Comp3..ete the adjustment of the instrument by correcting the circularspirit level by its own adjusting- &cre\rs0 This may be carried out after,accurately levelling as in para. 2«

In the ordinary course of work the instrunient is set up approximatelylevel with reference to this circular spirit level by manipulation of the tripodlegs and the foot screws a

4« Parallel plate microraeter test for run (S5QQ only)

This test Trill be carried out at least once a week* The level will beset up pointing one footscrew toxmrds the stavs at an approximate distanceof 100 fgste Accurately level in the normal v«?y? with the parallel plate fittedand set at zer-Oo The level hair is unlikely to coincide exactly with one ofthe a02 graduations | make it coincide (with the aid of the forward footscrew)with the lower of the two graduations i-»e« the apparent higher in the field of

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view of the telescope. This will cause a slight dislevelment of the mainspirit level which will not affect'the test for run. Now rotate the parallelplate micrometer through one complete revolution of 20, the level hairshould then coincide with the next 002 graduation. Should this depart from20 by more than +_ e001 i0e. 1 division on the drum, the instrument will bereturned to the instrument shop at HcC;. for adjustment.

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S&*VaSv,£ i^w •*5K? >-*•*-* *sx£,»<: :