What is the lowest and what's the highest ever recorded air pressure on Mars by an (either roving or stationary) Mars landing probe?
As per the answer in this question of mine, it seems the highest pressure record would have been measured by Viking 2 or Curiosity and the lowest by either Opportunity or Mars 3; though the latter landed at higher elevation it failed before doing much science so I guess the measured record would be Opportunity's. However, surface pressure varies throughout the Martian year.