I have been really distressed since returning to Alaska from St.
Auban a few years ago when I had to give up my very easy metric 20/1
glide calculator system for 1/250,000 maps, i.e., my right hand with
four fingers, and a metric altimeter.

Life should be so easy here. Here's why:

A hand's width, just above the knuckles, is 20k on my marked up French
road map commonly used for soaring in the Sud Alpes. So at 20/1, you
need 1,000 meters to glide your hand's width across the map. Two
fingers on the map to a safety field requires 500 meters plus pattern
entry height which I had already marked on my map. All I had to do
was to count my fingers to the landing field, multiply by 250, and
add the pattern entry height to know whether I had to buy a new glider
or not.

It doesn't get much simpler than that which is fortunate for me
because I can't do much more complicated calculations in my head,
especially when I am stressing because I am low and lost in the
mountains in a foreign country where the only people who speak worse
French than I do are my fellow Alaskans Jeff Banks and Ed Kornfield
who also flew from St. Auban. No GPS, PDAs, or complicated glide
calculators (formerly known as prayer wheels in the old days of
circular slide rules), just lay your hand on the map, count your
fingers, and add.

One note on French altimeters: In addition to being marked in meters,
the French, rather sensibly when you think about it, have the -0- mark
on the altimeter on the bottom of the dial and you go up from there.

Pete Brown
Anchorage


Also, 20:1 and 30:1 are useful numbers for most sailplanes. An ASK-21
will most likely do 20:1 and an ASW-20 will do 30:1 (though I used to
do 20:1 when over rough terrain or expecting strong sink). So, take
the distance in NM and multiply by 200 and you have 30:1. Multiply by
300 and you have 20:1. Granted, this would be just as easy in metric
units, but not the map measurements.

Someday, I just might have a complete electrical failure... and it's
nice to have a few mental tricks available.

-Tom