Explanation
This is a memorization aid to help you remember the steps to convert a Compass bearing to a True bearing, or the reverse. Take the first letter of each word: Can Dead Men Vote Twice → C-D-M-V-T, standing for Compass, Deviation, Magnetic, Variation, True. To go the other way, read it backwards: True Virgins Make Dull Companions → T-V-M-D-C, standing for True, Variation, Magnetic, Deviation, Compass. ("At elections" / "add whiskey" are just there to keep the sentence flowing.)