Accurately Measuring Blood Drops

How to accurately measure blood spatter in order to find angle of

impact (AOI) and point of origin.

Accurate Measurement

• Vernier Caliper– Instrument used to measure with a high degree of

accuracy

– Accuracy is very important for a murder case– Measuring blood drops requires high degree of

accuracy• YOU wouldn’t want to be responsible for letting a

murderer go free!!!!!

How to read Vernier Caliper

• Add pix

You Tube can help!!

• Video showing how to read a caliper (inches)– http://www.youtube.com/watch?v=Vz40xmrdhyY

Caliper Practice• Accurately measure to width of a meter stick at

your station.

• Accurately measure the width of a pencil at your station.

• Accurately measure the diameter of a marble at your station.

• Accurately measure the inner diameter of the roll of tape at your station.

Caliper Practice Answers• Accurately measure to width of a meter stick at

your station.

• Accurately measure the width of a pencil at your station.

• Accurately measure the diameter of a marble at your station.

• Accurately measure the inner diameter of the roll of tape at your station.

Measure Very Accurately

• Use Vernier Caliper• Measure Width• Measure Length (round off ellipse)– As shown in diagram

• Calculate Width/Length• Calculate sin-1 of the W/L (same as arc sin)

Angle of Impact

length

width

Angle of impact = arc sin W/L

Distance from point of convergence

Hei

ght a

bove

poi

nt o

f co

nver

genc

e

Origin

85 60 45 30

Angle of

Impact

90

10

70

2030

60 50 40

80

W

a

l

l

Floor

Path of blood

Determine Angle of ImpactWidth Length sine arc sine

2 3 .6667 42°

1 4 .25

9.6 9.7

14.5°

.9897 82.2°

Hand-out

By accurately measuring the length and width of a

bloodstain, the impact angle can be calculated using the SIN formula

below:

AOI = SIN-1 W / L

LENGTH = 5.9cm

WIDTH = 2.6cm

Finding AOI

SOLUTION:

AOI = SIN-1 W / L

AOI = SIN-1 2.6/5.9

AOI = SIN-1 (.44)

AOI = 26.2°