Where can I find the precise values for the peak frequency and wavelength of the Cosmic Microwave Background? I find rough numbers in the literature, reporting a frequency of 160.4 GHz and wavelength of 1.9 mm, but these numbers are obviously not correct because they are not consistent with the formula:
c(lightspeed in a vacuum) = wavelength times frequency
= .0019 meters times 160,400,000,000 Hz
= 304,760,000 meters per second
The widely accepted speed of light in a vacuum is 299,792,458 meters per second. This is an error of 1.65699365%. I need much greater precision for my current project.

Thanks for your help