...I might automatically be able to do this in my head...
Iceland's local time is identical to UTC all year 'round, and I know my timezone's UTC offset at all times, so I have
that down pat. (By the way, we all'll be having
one of those turns of the year again.)
Finland does DST - and since they're a EU member, I suppose their DST switching is pinpointed by the same
EU regulation as Germany's. Nonetheless, just adding a Helsinki entry to my clocks is simpler than doublechecking, so ...