Kenneth builds an enclosure and power supply for a “cheap” rubidium frequency standard. Rubidium standards are used for high precision clocks, and time keeping with a drift of only 6ms a year.
Normally, rubidium standards are very expensive, but it is possible to find these modules on eBay for $50-$100 as they come out of decommissioned equipment (such as cell phone towers, which need this level of time stability). On a hobbyist bench like my own, these standards are useful as a very good time base to calibrate other oscillators against. They’re also useful because 10MHz is the standard time base used by bench test equipment, so this standard can be used to drive frequency counters and spectrum analyzers via their time base ports so that they are more precise than with their stock internal 10MHz oscillators.