Setup
Deuce-to-seven lowball: the ace is always high, and straights and flushes count against you — so 7-5-4-3-2 is the nut and 7-6-5-4-3 is a straight. Give a seat five cards or leave it face down for a random hand, pick how many draws are still to come, and run it. Both seats then draw out the hand under the same policy, so the equity is the real thing rather than a showdown between frozen hands.
Equity
Run a spot to see win, tie and equity
Equity is win% plus an even share of every tie, which is what a pot is actually worth to you at showdown.
Improvement by draw round
What this hand can still become
The same five cards, priced with three, two and one draw left. Each column plays the hand out to showdown from that point, so the left column is worth more than the right one for exactly the reason you would expect — more draws, more chances to get there. The one-draw column is exact: every remaining card is enumerated, nothing is sampled.
Pot odds
Is the call profitable?
Fixed-limit sizing, in big bets. Equity comes from the seat highlighted above.
Pot odds ignore what happens on later streets — implied odds from the draws still to come, and the bets you will pay to see them, both move the real number. Treat this as the floor.