Measuring Bloodstains
My instructor taught me how to use a drafting caliper to measure bloodstains.
FIGURE 1 FIGURE 2
To measure a bloodstain, first take your caliper and adjust it to what you visualize is the widest part of the stain.
Next, from one side take your caliper and move it inward until the points touch the edge of the stain (Figure 1).
Afterwards, place two pinpoint marks to mark this position (Figure 2).
FIGURE 3 FIGURE 4
Do the same for the opposite end of the stain (Figure's 3-4).
FIGURE 5 FIGURE 6
Next, draw a line between these marked areas to locate the approximate middle of the stain and measure the width of
of the stain at this area (Figure's 5-6).
FIGURE 7 FIGURE 8
Take this measurement and place next to a ruler (metric) to determine the width of the stain, approx. 5.5 mm (Figure 7). Now, it's time to work on the length. On the previously drawn line, place one leg of the caliper in the middle of the stain and adjust the other leg outward to the edge of the stain (Figure 8).
FIGURE 9 FIGURE 10
Now, keeping the inner leg in place, turn the caliper 180 deg to where the outer leg moves to the opposite side of the stain (Figure 9). This time keep the outer leg in position and adjust the center leg outward to the opposite edge again. This is the approximate length of the stain (Figure 10).
FIGURE 11
Place your caliper next to your ruler to determine the approximate length of the stain, approx. 35 mm
(Figure 11) Result: W=5.5mm, L=35 mm, 5.5/35= 15.7, Inv Sin= 9.04 deg
References: Bevel, T. & Gardner, R., (2008) Bloodstain Pattern Analysis-Third Edition with an Introduction to Crime Scene
Reconstruction, 179-181.
I read an interesting article one day entitled "New Bloodstain Measurement Process Using Microsoft Office Excel ® 2003 AutoShapes" by Mark Reynolds; M A Raymond, Journal of Forensic Identification; Jul/Aug 2008; 58, 4; Criminal Justice Periodicals pg. 453.
I first thought, how cool is that; but how accurate is it? So, I figured I would give it a try and see what I thought.
I first scanned a blood drop stain to be inserted into Microsoft Excel ®. Next, I clicked on insert, picture, from file and navigated to where my scanned stain picture was and clicked ok.
Once the picture was displayed I clicked on AutoShapes on the bottom toolbar, then Basic Shapes and finally Oval.
Now, I have my ellipse.
The outline color of the ellipse was Black and the center was solid White; so I needed to change it to a more prominent color and make it transparent. I then right clicked on the ellipse itself and highlighted Format AutoShape.
By clicking on Format AutoShape it will bring up a dialogue box to make the desired and needed changes. You will need to change the fill color to No Fill so that it will be transparent when placing it over your stain. I chose the color Blue for my ellipse outline.
Next, simply highlight the ellipse, then left click and drag it over to your stain (placing it on top) and adjust to what you believe is the true ellispe.
Once fitted, I right clicked the ellipse again to bring up the Format AutoShape dialogue box.
If you notice at the top of this box it has tabs. Click on the Size tab. Here, you'll see the ellipse size, Height (or length in our case) 1.3' and Width .38'
So, now it's time to crunch some numbers. Height (Length) = 1.3' and Width = .38' which gives a Ratio of 29.2, Inv Sin= 16.9 deg
Finally, I measured the stain manually to make a comparison in results and came up with 16.3 deg. If my procedure is correct, I would say that using the AutoShape Function in Microsoft Excel ® is fairly accurate. This feature comes in handy especially if you cannot obtain the more expensive programs such as Hemospat and BackTrack.