# A chart for measuring angle and distance

This chart

works like Angle Cards.
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...

## Simplifying distance estimation for targets of accurately known size

The chart was motivated by a reader's interest in determining the
distance to archery targets of known size.
With the Angle Cards, if you know the target is say 1.16 yards tall, it
takes some work to tell the difference between a 23 and a 25 yard
distant target.
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.

## Links

Angle Cards - A "business card" for measuring angle and distance

Measuring Angle and Distance with your Thumb

**Thanks** to a reader, Lamar Fussell, for motivating this page.

Comments encouraged -
Mitchell Charity
<mcharity@lcs.mit.edu>

Notes:
Here is the xfig source for the first draft chart.
Doables:
Cleanup chart (generate with PS).
Add url.
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.
CGI draw
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.
History:
2001-Nov-07 Added name to credit.
2001-Aug-14 Created. Ripped from Thumb.