It seems clear that during cautious exploration underground, characters with 12" movement rate would move 240 ft over the course of a 10-minute turn.Exploration is conducted in turns of 10 minute duration with 1" representing 10ft. Thus a movement rate of 12" is reckoned to be 120ft underground with two such moves allowed per turn of cautious progress;
If all caution is abandoned (during flight or pursuit, for example) movement is quadrupled but mapping becomes impossible.
However, I'm not clear on the rate during non-cautious exploration. Is it 960 ft / turn (120*4 per move, 2 moves per turn), or is it 480 ft / turn (120 ft, 4 moves per turn)?
I'm judging the former, but just want to make sure.