So, I have some older topo maps (10 years or so) and want to know if I should use the current magnetic declination of today or do I still use the declination printed on the old maps?
OK, get to claim expertise here (geophysicist). You want the current declination because the map is drawn to geographic north. You use the declination to adjust the compass from magnetic north (when you use the compass) to geographic north. If you use what is on the map, you'll be off some amount. If using a c. 2000 topo map, probably close to your ability to read a compass and not a big deal (maybe 2° off). If using a 1955 topo map, things start to get more significant (~6° here in the Denver area). You can get the current magnetic declination from this NOAA website . Many phone apps have corrections for declination built in.
Your map is only ten years old?? In one of the areas I frequent, the topography is based on aerial photography taken in 1938 (some of the earliest in the US) and published in 1943....
Let's say that for whatever reason, you don't have access to the NOAA website and you don't know the correct declination. Wait until nightfall and the appearance of the North Star ( you are in the northern Hemisphere, right?) Th north Star is always within a degree or so of true North - I believe at midnight it is precisely aligned. Align N on your compass with the N star and read off your magnetic declination, since your needle is pointing to the ever wandering magnetic north pole .
Since I am usually in country with fairly rugged relief, I usually don't bother with a compass at all, but simply align my map with the topography. This works great about 98% of the time, until visibility is diminished by fog or storm, then the compass is ALL IMPORTANT!!
Compasses are also useful when wandering in a Kansas cornfield or in many open water situations. I always have mine handy, even though seldom used....
Thanks I appreciate your help. This solves an old problem and finally answers a question I’ve been asking for quite some time. Now I feel more confident using my older maps by just using current up to date declination vs the one printed on the map. Thanks again for your help