I had been looking at a way of checking calibration of my DMMs on DC, and this useful board will do that for £4. Using an AD584K Precision reference chip, that will output 4 high stab Volts by the flick of a switch:
10.0 V +/- 10 mV
7.5V +/- 8 mV
5.0V +/- 6 mV
2.5V +/- 3.5mV
Figures quoted are for 15V feeding the input of the board
I have seen these on the Internet at various sources, but my link proved to be the cheapest I could find: http://www.banggood.com/AD548-High-Precision-Voltage-Reference-Module-4-Channel-Calibration-p-932160.html
There is also a full spec sheet on the device at the above link.
I will come back to this when I have boxed it up and terminated it for better protection..