Read the reveal: what the score and the percentage error mean
After you lock in, the reveal shows three numbers: the recorded measurement, your estimate, and a score out of 100.
The 6 % band
If your estimate is within 6 % of the recorded value, you score the full 100. That band is deliberately tight; it rewards a correct ratio and a correct unit.
Beyond the band
Outside 6 %, the score falls with the multiple of your error rather than the raw difference. Being a fifth too big costs a little; being twice too big costs a lot; being 5 times too big or too small scores nothing at all. A guess of half the true size loses exactly as many points as a guess of twice it.
Why multiples?
Scale is multiplicative. Doubling and halving are the same size of mistake, whatever the object. Scoring on multiples keeps a round about giraffes as fair as a round about mountains.
Reading your 5 blocks
Green blocks are 85 or more, amber 50 to 84, red below 50. A row of greens with one red usually means a single mis-read dimension, not a bad eye.