⚛️🕰️⏱️

#rubidium #atomic clock #frequency standard #timekeeping #rb clock

⚛️🕰️

#atomic clock #time standard #frequency standard #NIST-F1 #microwave resonance

⚛️⏰🛰️

#NIST #national institute of standards and technology #atomic clock #time standard #official time #frequency standard #NIST-F1