Hi there. Listen, would someone just like to check my maths? ;-)

#declare FPS = 25; // Simple enough...

#declare TotalTime = final_frame / FPS; // = total number of seconds?
#declare TimeStep = clock_delta * TotalTime; // = seconds since prev frame??

Assuming I got that much right, how about this for my air resistance damping
bit:

#declare Velocity = Velocity * (1 - (k * TimeStep));

(where k has already been defined as something like 1e-2 or so).

I just tried my simulation at two different frame rates and got different
results. However, this doesn't mean the formula is wrong (IMHO), since the
orbit I'm calculating is highly unstable; the result is probably different
with the original one too! (i.e., the one without air resistence.) Anyway,
the results _look_ fairly good - will post to the animations group as soon
as POV-Ray finishes drawing it ;-)

Andrew.

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