Thought I'd just made the point that, as the met man tells big pork pies anyway, i don't see much point in converting true wind to magnetic!
And as regards "showing your workings", the last time I did that was at University, it has no place in puddlejumper navigation. A quick clock rule / max drift MDR of the drift is well within the mental abilities of anyone who deserves to hold a pilot's license of any description.