Algodoo

this one shows the y - azimuth , as you can see the aircraft does not ' know ' the value of the maroon circle which represents the vertical curvature of the earth [ not horizon line ]

but it does know the exact value of the gold circle which is relative to its main circuit component .

the smaller blue circle between them is an ' arbitrary ' calculation that saves the computer time , allowing it to perform a greater number of final calculations per 2 billion / pentafloop .