I have made a bold decision today. I have decided to retire my “Fundamental Physical Constants’ card from my wallet. This particular card has been in my wallet(s) continuously since 1986. I had an older version from 82-86, and this replacement was an exciting upgrade at the time. Over the years you might be surprised at how many times is was a valuable reference.

It is interesting to look at the values to appreciate how ‘constant’ they have been. For example Boltzmann’s constant is listed as 1.380662 e-23, while the exact defined value is now 1.380649 e-23. Many of the constants have been improved on over the last 35 years.

Some of the constants, like the above Boltzmann’s constant, Planck’s constant, elementary charge, and Avagadro’s constant are now defined as exact values. These were all a result of the monumental change in 2019 of defining the remaining SI units in terms of these constants, instead of based on measurements. (the kg, ampere, kelvin, and mole).

As mentioned on the back of the card, the previous system relied on the physical prototype kg stored in France.

Some things, like the fine structure constant are dimensionless and have been improved upon significantly over the years.

It is certainly a bygone era to have a printed card like this, but it served me well.