I’ve not heard of CDMVT before, so I did some research. This is slightly new to me because I’ve not done navigation on a ship, only while hiking where there is no ship.
All information on a chart, including your own plotting, is related to TRUE North. Thus all bearings on a chart are related to TRUE NORTH.
Compasses point to MAGNETIC NORTH, which varies from True North by an error called VARIATION. Compasses also are subject to their own errors; this is called DEVIATION.
COMPASS BEARING = TRUE BEARING +/- MAGNETIC VARIATION +/- COMPASS DEVIATION
Can dead men vote twice at elections - CDMVTE The mnemonic device helps you remember the steps to correct a magnetic compass to true OR a true compass to magnetic.
So if you start with a compass reading, you convert it to a magnetic reading by adjusting for the error in the compass. Then, you convert to the true reading by adjusting for the variation.
If you are going from a chart to a compass, the steps are taken in the reverse order.