Haha, my friend was grilled for this in his honours thesis defense. He was doing solid-state caesium NMR, and referred to the spectrometer as "the 600". One of the professors asked him, "You mentioned the 600MHz spectrometer, but that's the resonant frequency for protons. What is the resonant frequency for the nucleus of interest in your research?"
What's constant between the nuclei is the field strength of the magnet in Tesla. From there, you want to find the Larmor frequency? I don't remember all of my NMR theory. Anyhow, a quick way to find out is to look at an NMR printout from the spectrometer. It should give you the frequency lock.