Is this a sensible way to do it?

Of course, it's me rather stupidly thinking I should compare it to getGunHeadingRadians() instead of getHeadingRadians() - the signing I already worked out was the wrong way around, but thank you for pointing that out too.

I don't know about providing any competition, but I'll give it the best shot I can! If I can ever grok Wave Surfing...