Hydrogen
At the moment, Wikipedia should be the better source!
Skipping on un-necessary formulations : TIME
The Hydrogen Second is at around 0.7 seconds ([Hydrogen Cycle]*10^9) as closest pragmatic unit, thus also referred to as HYDRON.
1 Milli Hydron = HC*10^6
1 Micro Hydron = HC*10^3
1 HC = 1420.40575177 MHz = 1.42040575177 GHz = 1/(1.42040575177*10^9) seconds
1 HYDRON = 1000/1420.40575177 seconds