On skyvector, the correction, for magnetic heading, that comes up doesnt always match what the agnostic lines dictate.
For example a direct, true course, from KBOS to KALB is 282. Both when I plot it and when I do it on skyvector. However on the chart the magnet var is about 14.5W. Skyvector says magnetic course is 298, a 16 degree difference.
Its not a big difference, but I'm planing my first cross-country (not from KBOS to KALB lol) solos and its a bit confusing.