Ihave beenworking on measuring deer to calculate their distance manually without the use of a rangefinder. I'm sure this wheel has already been invented, but has anybody had any luck with it. I just finished yesterday and here are the results if anybody is interested.
When I list target size I do not mean shot placement size or vital size, I only use target size to find range of deer.
Target size of blacktail deer is 16 inches average. This is one of my constants.
The second constant is the range my sight pin gaurd is from my eye. For me it was always 34 inches at full draw. This is an important measurement and will be different for each hunter. Measure yours to see what it is before measuring target size.
Third step was to measure height of target (16 inches) with a digital caliper 34 inches from eye at ranges from 10-60 yards.

Here are my results:

10 yards 1.750 inch
20 yards 1.00 inch
30 yards .650 inch
40 yards .500 inch
50 yards .350 inch
60 yards .285 inch

Now all you have to do is make 1 mark on your sight housing about the 10 o-clock position. Make mark as bright and as thin as possible. This will serve as your master mark that all other marks will relate to. This mark will also be placed on top of deer back. Measure down sight housing and make a second mark for your 10 yard range of 1.750 inches below top master mark. The third mark will be 1 inch below master mark and the forth mark will be .650 of an inch below top master mark and so on. Put up a target that is 16 inch in height from backbone to brisket. Go out in a field and walk anywhere from 10 to 60 yards. Stop and align the deer between whatever mark fits him best. This will tell you his distance from where your standing. Once the distance is calculated you will know what pin to use or proper hold-over to engage target. Sounds crazy but once the marks are placed on your sight housing, it only takes afew seconds in the field to determine what range the deer is at.

Keep in mind if your measurement from sight pin housing to your eye is not exactly 34 inches at full draw the above measurements will not work for you. If you have a shorter distance then all your measurements will be smaller than the ones I listed above.

If any of this info helps just one person I'll be happy. Just sharing what I recently learned, hope it helps you in the field. Any better ideas would be appreciated.