On Fri, Apr 14, 2017 at 12:01:17PM -0700, Trent Piepho wrote:
> I've got to wonder why some are offset by -90 degrees and some
> aren't?

Sign of y input.

Most code has pattern atan2(x - mx, my - y), but code for torpedo
guidance t_track in ntserv/daemon.c uses atan2(x - mx, y - my).

Further uses of dy in t_track don't stop us from changing the sign in
order to remove the offset.

(t_near and t_explosion makes the same calculation of dy but there the
sign does not matter.)

James Cameron