500
If the speed of light was 300,000,000 m/s rather than 299,792,458 m/s, how much would the length of 1 meter change by?
299792458/300000000 = 0.99930819333
The new meter would be ~0.99931 old meters long, as there would be a 1/1444 decrease in all lengths since all wavelengths would be reduced.