The keypad works numerically, with the [#] button for enter.
If you wanted to enter a decay time of 2.6 seconds, you can either:
highlight decay and press the [+] or [-] 'nudge' buttons until you reach the required number
or you can press the 'pot' button (for decay time only, I recall... the pot is the single most useless control on the face of the unit...) and turn the dial until you get to 2.6 seconds
or you can press [2] [.] [6] [#]. (two-point-six, enter)
That's all it does.
Saving gives you nine glorious memories, 1 through 9. You press save, then a number flashes, indicating the number it is going to save to. You either press [#] (enter) to okay the selection, or press a different number and press enter.
Recalling is the same: recall, followed by enter (if it's flashing the number you want) or recall (the number you want) followed by enter.
Later software issues had 12 memories. Programs created by the remote could be stored in 10-12 only. I forget if there were user registers or program registers though.
We got our first RMX-16s in the early 1980's, and it took about 5 minutes with the first one to work everything out, with no manual.
the memories are pretty much not needed. All you have is program number, decay time, predelay and HF/LF filter. Some programs don't even have all of those. Many of the programs were never used. I don't think that any clients ever used the chorus, delay or echo programs. The plates and halls sounded rather un-musical, the room program (there was only one) was scarcely if ever used, and the reverse and nonlin were mono. reverse 2 and nonlin 2 were stereo, but the reverse was unfriendly. That left Nonlin and Ambience.
Every time you walk into a control room with an RMX-16 powered on, it ALWAYS has either ambience or nonlin on the display. That's because that's about all the box does. For a long time, it was KING of both of those jobs, and I've still never actually heard anything that sounds like the RMX16 nonlin... There might be decent copies, but I've never heard one.
Basically if you want the "Billy don't you lose that number" Phil Collins snare sound, you have to have an RMX16 (which was the stand-alone evolution of the DMX-15, a similar-looking box which had to be hooked to a DMX-15-80 (NOT 15-80S) which is used as the input, output and ram buffer for its processing.
Ultimately, these things break down, and we were VERY lucky to live about 45 minutes drive from the buy who built them at the AMS factory. Nowadays, here in the US, I wouldn't get one unless it was VERY cheap (I'm talking sub-$200) because sooner or later it WILL need a repair that won't cost less than $1000, even IF you can get the parts...
That's my condensed familiarity with the RMX16 as far as I can call to mind in a few moments... -If I think of more, I'll post more.
Keith