"In general I planned to handle the "within 10 cm" thing during analysis. Try to fermi estimate the value and give your closest answer, then the probability you got it right. We can look at how close your confidence was to a sane range of values for the answer."

But unless I'm misunderstanding you, the size of the unspoken "sane range" is the entire determinant of how you should calibrate yourself.

Suppose you ask me when Genghis Khan was born, and all I know is "sometime between 1100 and 1200, with certainty". Suppose I choose 1150. If you require the exact year, then I'm only right if it was exactly 1150, and since it could be any of 100 years my probability is 1%. If you require within five years, then I'm right if it was any time between 1145 and 1155, so my probability is 10%. If you require within fifty years, then my probability is effectively 100%. All of those are potential "sane ranges", but depending on which one you the correctly calibrated estimate could be anywhere from 1% to 100%.

Unless I am very confused, you might want to change the questions and hand-throw-out all the answers you received before now, since I don't think they're meaningful (except if interpreted as probability of being exactly right).

(Actually, it might be interesting to see how many people figure this out, in a train wreck sort of way.)

PS: I admit this is totally 100% my fault for not getting around to looking at it the five times you asked me to before this.