L Peacock,
For once, I stand corrected with on my RB199 knowledge!!
It is indeed Trim Datum Bias. I applaud your memory of such mundane TLA's!!
I did actually have to go and break open my Cottesmore Tornado School Notes then!! And in honesty was confronted with page after page of "Lowest Fuel Wins" notes that I'd hoped to forget years ago!!
I'll trade you your "Trim Datum Bias" tweaks for a good old Hot Shot clean though!!
Regards,
Flipflopman