Calculating a 1RM is typically done by the Epley Formula and it’s just an estimate. One equation is probably as good as the other. This chart is just based on an equation, nothing more, nothing less. Knowing the equation eliminates the need for the chart.
To calculate the 1RM I would multiply reps by weight to calculate volume, then volume by .033, add that number to the original weight.
Say my 5RM squat is 315. 5X315 = 1575.
1575 x .033 = 51.9
If you have a 1RM and want to figure out what your 5RM is, you can just change up the equation.
367 x .033 = 12. Multiply 12 by number of reps, in this case 5, 5x12=60.
367-60 = 307. Not exactly 315, but close.
Mindless drivel for you to consider.