Optical frequency combs are another one of those bits of magic. If you have the means, you can buy this optical comb frequency counter[1], which can measure the

Optical frequency combs are another one of those bits of magic. If you have the means, you can buy this optical comb frequency counter[1], which can measure the frequency of light to 14 digits of accuracy, so within 10 cycles per second! [1] https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_ID=11422 https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_ID=11...