[Skywave]

David: thank you for your contribution in post #5. The i.c. as featured in that post does indeed look promising - plus the availability of a suitable pcb. Definitely a strong contender here.

You also say "Not having a precision Voltage Reference hadn’t left a gap in my life, but as a compulsive builder of bits of simple test gear, I thought "Why not?" "

That is something I can readily relate to - and indeed think the same way.

Unlike many other branches of engineering, when we make a measurement in electronics, we are almost invariably measuring the effect of, say, an electric current, and the resultant indication follows. Hence, there is the 'concept of trust' in that: can I trust that measurement? Knowing that you can gives a sense of assurance that you are on the 'right track' when repairing or designing something. In actual point of fact, (and in my experience), these are some occasions when small measurement errors are not ignorable.

Al.