i will try to answer my own question-

(1) absence of a number in the move order could be the equivalent of a "0", meaning application of enough thrust to negate vector of motion from last move

(2) as there is no indication of the ability, or need, to write "-3" in a move order, (1) must be an operative statement

(3) under these conditions, and likely as a matter of simplification, it is impossible for a ship in Starmada to conduct retrogade motion with respect to its front facing

seems logical to me anyway

lamont

One could, I suppose, easily add the option to allow "negative" movement.

e.g.,

My previous speed is 6.

My current plot is "-3P1" for a new speed of -2 (-3 + 1).

The nice thing about this is that it wouldn't change the thrust requirements at all...

Okay, I'm no Starmada guru, but I believe the resultant thrust from this turn's move affecting the next turn's move would be as he has shown (the movement before the turn plus the movement after the turn): -3 + 1 = -2.
In this way it's no different than if you'd plotted a 3P1. The resultant thrust affecting the next turn's move is: 3 + 1 = 4.
However, he didn't address the thrust requirement necessary to complete the maneuver. I'd think that would fall into a new category of adding all thrust together, regardless of whether they're positive or negative. So I'd think the thrust requirement for the example maneuver would be:
6 + [-(-3)] + 1 = 10.
That's just a guess though.
Kevin

I play hexless and use a FT vector system (which is simple but a bit fiddly as you have to have a marker chit to show heading) or more recently the cinematic system (which whilst less 'realistic' avoids the jousting contests that often ensued).

If I used hexes (we are planning to try thm out soon) I rather like murtalians system. Simple and easy to grasp. It doesn't take into account facing vs heading and the latency involved in rotating a ship.