Obstacles(towers, etc.) on app plates are MSL? If not AGL how do you measure an obstacle in MSL? I understand that MSL is the only useful number to an IFR pilot concerning an obstacle.

Thanks in advance!

All obstacles are charted in MSL, except for those in the Take-Off Mins pages where they are charted MSL/AGL. The AGL is referenced to the airport elevation or runway elevation.

GF