There are charts that cover what I'm referring to. Look at:
Footprints by Dish Size - Latitude Declination Chart - C/Ku-Band Satellite Listing
At this page, there is a chart for declination and a chart for "modified" tracking angles, which is the more accurate values. (Note, this chart incorrectly refers to the latitude value as being an elevation, when actually the elevation is 90 minus this value).
The declination of a sat to your south is very easy to calculate, which is why most charts (such as you'll find on the
Sadoun site) use these values. I just drew up a little picture describing the calculation.
Basically, the declination angle is the "d", which is described by a right triangle with one side being the distance above the earth's equatorial plane you are located ( "A"), and the other side being the distance to the sat in the equatorial plane, ( H + C ).
The problem is that the declination of sats toward either your east or west horizon is less, up to about 0.6 degrees less, so if you use the south declination, you will be off by up to 0.6 degrees in your aim on other sats. I drew another diagram from the perspective above the north pole with south up.
For sats not to your south, the declination calculation still has the same "A" dimension, however the ( H + C ) dimension has increased, which is what causes the declination angle to get less. BTW, the DL angle is the delta longitude, ie the difference between the sat's longitude and your longitude, and the U angle is the so called USALS angle, ie the actual angle that the motor shaft has to turn to go to a satellite. But back to the declination, I can't remember the equations off hand, but I always look up the equation for calculating the angles of a non-right triangle, given two sides and an angle. Years ago I used to just spit that out from memory, but with age, I generally struggle for hours trying to do the calculations.
HOWEVER, a pretty good approximation for the declination angle for sats to your east or west is obtained by using ATAN ( A/(H+RE) ).
Basically, if you use this smaller declination, you have to increase the latitude setting on your motor by the difference between the south declination and the east/west declination, and this will correct the setting on south satellites, and the motor elevation's effect decreases proportionally as you motor east or west since it is orthogonal, so it is still correct to the east or west.