Table 1.

Interference microscope measurements of five green–orange reflecting (type I) and five dull purple (type II) scales. (Measurements in nm.)

measurement	type I	type II
path difference (air)=d(ns−1)	322.8±9.6 (s.d.)	293.6±9.4 (s.d.)
path difference (oil)=d(ns−1.516)	27.2±4.2	34.4±4.7
thickness d=(pdair−pdoil)/0.516	572.9±22.3	502.3±19.9
ns=(1.516pdair−pdoil)/(pdair−pdoil)	1.564±0.008	1.584±0.011