To get mildly
on-topic, I believe there's a TTL IC on one of the
boards in an RK05 that is powered between a +10V line (generated o
nthat board) and the main +15V line.
Here's another case where "there is no such thing as ground" can fail:
what you outline works only if there are other loads on the on-board
+10V line that collectively draw more current than the TTL in question
does. (Loading internal to the circuit generating it counts.)
Sure. In other words the 10V line needs to sink current (from a higher
voltage point) rather than source current (towards a lower voltage
point). You have to take some care in the design of the cirucit that
supplies this 10V rail (as you imply), but that's not difficult once you
realise the problem, and it certianly doesn't stop you calling any point
oyu likew in the circuit 'ground'.
-tony