tggzzz - is that the main ref x-tal just sitting on the pcb - would a little overcoat (thermal insulation) help its stability?
I believe it is, but that attempting to improve it would be like putting lipstick on a pig.
There is some form of (irrelevant) option to remove that XTAL and insert a "better" reference on an internal PCB.
More irrititatingly, it looks like there are poorly understood (RTFM? Wazzat?) limitations on the "ratio a/b" measurements with B=10MHz It appears that the ratio is inoperative over ~20MHz even though stuffing the same 10MHz input into the "external ref in" back panel socket allows "freq a" to measure 100MHz as expected.
Not sure I can be bothered to work it out. Tomorrow is a
long trog to pick up the scanning tunnelling microscope and a leopard. I hope I'll be able to dodge the unseasonably inclement weather.