  We have built a high-accuracy wavelength meter for tunable lasers using a
scanning Michelson interferometer and a reference laser of known wavelength.
The reference laser is a frequency stabilized diode laser locked to an atomic
transition in Rb. The wavemeter has a statistical error per measurement of 5
parts in $10^7$ which can be reduced considerably by averaging. Using a second
stabilized diode laser, we have verified that systematic errors are below 4
parts in $10^8$.
