In some contexts, the number on the napkin was the prize of the evening -- an attractive person of the opposite sex had responded to witty overtures and winning ways, and graced one with a phone number to be used for later conversation and arranging another meeting.
Nowadays, of course, one gives someone else one's digits, usually entered into a cell phone. As in the days of the desired napkin, those might be false -- but a quick call can show that even before one leaves the bar, so that alternative targets may be selected.
Physicists are not like other people. During December 2013, a group of them gathered at a bar and they also wrote down numbers on a napkin: Their best guesses as to the final estimate of Planck's Constant that would be generated by their particular project.
The group worked with the National Institute of Standards and Technology (NIST), which was trying to measure the constant in order to help redefine the kilogram. Earlier definitions relied on the International Prototype Kilogram, a physical object created in the 19th century to be the standard weight. Over time, its weight and mass have varied -- not enough to make much of a difference when someone stands on the scales or smuggles cocaine but more than enough to hobble scientific experiments requiring precise measurements.
At its 2011 meeting the General Conference on Weights and Measures decided to redefine the kilo in terms of Planck's Constant. Different groups have been experimenting to find more and more exact figures for the constant, and when the NIST group made the most accurate determination to date back in 2013 the team gathered to celebrate.
During the celebration, the ten gathered wrote down their own guesses as to what value would eventually be submitted to the General Conference:
The napkin was sealed in a plastic bottle and put into the foundation of the next level of the project, NIST-4. Recently, the project was able to make a determination of even greater accuracy with its NIST-4 device, and checked the numbers against the final submission. Shisong Li of China (5th from the bottom) earned the prize, as his guess of 6.62606990000 × 10–34 was closest to the submitted value, 6.626069934 × 10–34.
Another celebration followed, this one featuring a rum cake with the submitted value in icing. In some areas, it seems, physicists may be quite a bit like other people.