In article ,
Judah wrote:

Jose wrote in
. com:

The 90/270 has a tremendous advantage when making turns and
remembering where to turn.

The system is called the 'sum of the digits'

Take any number of the heading indicator and add all three of
its digits and keep adding until you get a single digit... (math
snipped)


Cool piece of math (even more interesting =why= it works, and how it
translates into other bases). However, to find my entry, I just look
at the DG and pick the number that's off to the side. I turn there,
then turn opposite onto the course. No math needed. The ten degrees
one way or another doesn't make any difference.

Jose

Because you're adding 90 to the numbers each time, and our math system is
10-based. If you add 9 to any number in a 10 based system, you are adding
1 to the 10's digit, and subtracting 1 from the 1's digit. The result is
if yo uadd the new digits, they will equal out.

It's easier to see if you take a single digit number, add 9, and add the
digits... It will illustrate the same point.


1 + 9 = 10 1+0 = 1
2 + 9 = 11 1+1 = 2
3 + 9 = 12 1+2 = 3

I used to know enough math to be able to solve differential equations
(well, the easy ones anyway), but when I'm flying an airplane in the
clouds, I don't want to waste any of my limited and precious remaining
neurons on subtraction.

The way I make a 90 degree turn is:

1) Move the heading bug until it's pointing sideways.

2) Turn the plane until the heading bug is pointing upright again.