One of the most frustrating hobbies I ever had was archery, but not because it’s hard to hit the target on the wall (it is, but I got pretty good at it). My problem was that one of the popular ways to go out and have fun with archery was to do “3D shooting”, where you would have to shoot at a series of animal statues, each placed at an unknown distance.
Estimating the distance turned out to be my downfall. If you don’t have a good idea of how far away the fake deer is, you’ll end up shooting over their back or burying your arrow in the ground under their feet. At the time, I assumed that estimating distance was less of a learnable skill and more of an intuition. Hence my surprise when I recently came across a quick trick of the eye and mental math that allows anyone to estimate distance quite accurately.
The technique involves some estimation at the intestinal level, but a much easier type. Then you just multiply by 10. Here’s how it works:
- Hold your thumb out in front of you (with your arm fully extended) and close one eye. Align your thumb with an object whose size you have some idea of (for example, a car).
- Without moving your thumb, close the open eye and open the other. Your thumb will appear to be in a different place.
- Estimate how far your thumb has “moved” relative to the object you are looking at. For example, a car is about 4.57m long, so if your thumb moved half the length of a car, it’s about 2.29m.
- Multiply by 10. In this example, you would calculate that the car is about 22.86m away from you.
Too good to be true? I went around and tried it. I also brought a laser range finder and tape measure with me to check. One thing I noticed right away is that I was tempted to measure the space between my two thumb images; instead you should measure from, say, the left side of the first thumb image to the left side of the second thumb image.
Standing in the kitchen, looking at the television in the other room, I estimated that the television was between 3 and 1.22 m wide, and that my thumb moved a little more than half its distance, about 0.61 m . Calculation: the TV must be 6.10 m away. Laser level says: 7.62 m. OK not bad.
From my desk to a nearby bookshelf, my thumb moved 6 inches, maybe a little more. Calculation: 60 inches. Actual Measurement: 59 inches.
From a spot on my driveway to a garden shed: I turned my head and sideways to measure the height of the gate. The thumb distance should be about 6 feet (most of the height of the door), so the shed should be 60 feet away. Actual measurement: about 21.34 m. Not perfect, but once again, not too far off.
The reason this trick is supposed to work is that the distance between the eye and the thumb is about 10 times the distance between one eye and the other. I also measured this. Looking in the mirror with a tape measure in front of my face, my pupils are 2 and 5/16″ apart, or 2.3 inches. The distance from the point between my eyebrows to my extended thumb is 23.5 inches. That’s a factor of 10.2, impressively close to the 10 I was promised.
Bottom line: This trick won’t give you an accurate distance, but as an estimating tool, it really works! And by the way, if you ever need to estimate how far away a deer-shaped statue is: the body length of a deer is about 1.52m.