Accurately Measuring Blood Drops

1. Accurately Measuring Blood Drops How to accurately measure blood spatter in order to find angle of impact (AOI) and point of origin.

2. 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!!!!!

3. How to read Vernier Caliper • Add pix

4. You Tube can help!! • Video showing how to read a caliper (inches) • http://www.youtube.com/watch?v=Vz40xmrdhyY

5. 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.

6. 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.

7. 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)

8. Origin Height above point of convergence 85 60 45 30 Distance from point of convergence length Angle of Impact width Angle of impact = arc sin W/L

9. 80 90 10 60 50 40 70 20 30 Angle of Impact Path of blood W a l l Floor

10. Determine Angle of Impact Width Length sine arc sine 2 3 .6667 42° 1 4 .25 9.6 9.7 14.5° .9897 82.2° Hand-out

11. 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

12. EXAMPLE Finding AOI LENGTH = 5.9cm WIDTH = 2.6cm

13. SOLUTION: AOI = SIN-1 W / L AOI = SIN-1 2.6/5.9 AOI = SIN-1 (.44) AOI = 26.2°