But instead of using your arm measurement to choose among different cards, here you simply fold the chart.
This can be more convenient than the cards when you are, for instance, calibrating a bunch of peoples' thumbs. But its main motivation was...
With this chart, if you know the size of the target, and the target is about one yard big (or meter, or whatever), then you can simply look up its size in a table, get a "compensating arm length", fold the chart in a slightly different place, and then hold up the chart and just read the distance off the "x" numbers. Just as if the target was exactly 1 yard big.
If you are going to be repeatedly dealing with targets of the same size, you might want to take the "compensating arm length" and get, or make, an angle card for it.
The chart graphs (actual height on paper = arm length / the x number). This version was quickly hand drawn, so there may be a bit of sloppiness.
Thanks to a reader, Lamar Fussell, for motivating this page.
Here is the xfig source for the first draft chart.
Cleanup chart (generate with PS).
Variant explicitly targeting archery?
Extend to low x numbers? Nice to be able to use meters indoors.
Add degrees and rad? In color?
Add support for imperial units (arm inches)?
Search engine fodder: range finder.
an "x" rule given an eye-to-ruler distance. See cards. But bigger.
a distance rule given an eye-to-rule distance and object height.
2001-Nov-07 Added name to credit.
2001-Aug-14 Created. Ripped from Thumb.