An oil well contains water at the bottom, oil floating on it, and air above the oil. You performed two time-of-arrival measurements with an instrument that measures the depth of the well using a light beam. The first reading on the instrument is 1; = 1.33 us and the second one is 1, = 1.29 us taken after a certain amount of oil was pumped out.

Calculate the change in the oil level considering the oil refractive index is 1.46.