Taking this relation into account, the minimal uncertainty, Δ Δ x m e a s , the light pulse should have in order not to perturb the mirror too much, should be equal to Δ Δ x b . a . yielding for both Δ Δ x m i n = ℏ ℏ ϑ ϑ 2 M . Thus the minimal displacement measurement error that is prescribed by quantum mechanics read: