I guess I could use my calibrated remote magnometer equipped D10a to swing my whiskey compass and have the compass correction card apply to it.
Would I have to also display a 0/0/0 correction card for the Dynon?
A couple of thoughts here...
1) not sure where the 0/0/0 idea is coming from. We are allowed to have errors as large as 10 degrees, or larger than 10 degrees if caused by operation of electrical equipment such as windshield heaters - just note what causes the exceedance of the 10 degree limit
2) do not for a moment believe your Dynon will be perfectly calibrated to zero degrees of error on every heading. Magnetometers generally are pretty good but also generally still cannot correct for all errors.
3) Calibration of a compass requires a "known good" reference. That reference can be a compass rose which is properly maintained (many at airports have not been corrected for the drifting magnetic poles in many years thus they contain a "built in" error). Another reference is a calibrated master compass. A third reference more commonly available to us is a cross-check of heading indication versus GPS-derived ground track while taxiing (NOT while flying, thanks to wind!). It's difficult using this method to calibrate headings every 30 degrees unless the airport has a large flat surface suitable for stable taxiing in multiple directions.
Coming back to the CARs requirements, if an aircraft has a whiskey compass, that compass can be calibrated and a calibration card posted in the cockpit. Great - no problems there.
Where it gets a little more tricky is when we have opted to use an EFIS and have no whiskey compass. That's when we have to meet the guidance outlined in the excellent MD-RA C-18 document. And the kicker is that, if you have multiple EFIS systems using multiple magnetometers, each of them must be calibrated and a calibration card posted in the cockpit.
Interestingly, I have dual magnetometers literally stacked one atop the other in precisely the same orientation and, of course, in the same magnetic interference environment. These two magnetometers produce surprisingly-different results after following the manufacturer's calibration procedures. The manufacturer hasn't yet been able to explain to me why there may be as much as 7 degrees difference between these two sensors. That's just the way they are. Luckily I have a whiskey compass which is calibrated and for which a calibration card is posted in the cockpit.
Technically speaking, Transport Canada, if they ramp check, can snag an aircraft where its compass calibration card is missing any vital information including the signature, date and license number of the person certifying the compass calibration data. That piece of paper is tiny, so write the excess information on the back side!