The frequency setting accuracy of the waveform generator is 1 µHz.
Unfortunately that says as good as nothing about the accuracy of a waveform generator. It is a setting resolution specification, not accuracy.
Yes, maybe I was a bit too hasty with my answer. You are right, the 1 µHz is the setting resolution.
The built-in reference clock is specified with an accuracy of +-2 ppm (+-3 ppm after one year of aging). If you use an external reference, the accuracy will of course depend on the external reference.
Regarding the DDS resolution: The Magnova generator currently works with 62 bit DDS resolution. The 400 MSa/s generator sample rate divided by 2^62 allows values far below µHz. In addition, the maximum internal phase value is matched to the output sample rate (400 MSa/s vs 375 MSa/s) to achieve best frequency precision.
It would be very interesting to see the internal solution for the placement of the heat dissipation components.
The external part of the heatsink looks quite small from what I saw. Or maybe the whole back panel is actually a heatsink.
Yes, the entire metal housing serves as a heat sink. The additional external heat sink is located at the hottest point, with the FPGA/processor/RAM underneath.
Sorry, but it's difficult to show this in a photo, the built-up doesn't allow a clear view of the relevant area. The components are thermally bonded directly to the rear panel. I could take photos of a completely disassembled prototype, but that wouldn't provide much more information on the question.