You may reset a puzzle by backing away and then
zooming in again.
Wait until all three keys are in your inventory before
cracking a Three-Key Safe. If you insert fewer than
three keys and attempt to leave them there while searching
for the remaining keys, you will lose the ones you inserted.
In Room 5 (the Constructor's Office) zoom in on the drafting
table to the right of the safe to disclose a diagram of
Abraham's Switch Safe.
In Room 21 (the Kitchen) zoom in on the controls on the
Refrigerator Safe. To open it, use the temperature formulas
above to calibrate the mechanism.