I posed this question to a
PhD friend of mine. His reaction:
"5: "walk up the stairs and use the barometer as a ruler to measure the height of the walls in the stairwells."
I like this one. Then you have the height in barometers, or I guess that should really be barometREs. If I remember correctly, "baro" is latin for 0.17643258, so one barometre equals about 17.643258 centimetres.
He's so full of trivial information. No wonder I like him.