Sounds familiar.
Wikipedia sums up the log notation nicely. However, they don’t include tax authorities’ preferences.
Either way, the initial survey lacks “yes” as an option 
. One reason I made a table for a range of income (and a bar chart for my spouse) back then was to calculate the impact of pillar 2 buy-ins. If you use this option, and as long there’s enough limit left, you can basically pick your desired marginal rate for a while.
I challenge the statement that in maths it is common to use log to mean natural log. Mathematicians are lazy as hell and for sure will write ln\ x instead of log\ x or log_e\ x whenever possible.
So I’ve been caught at least 3 times by this!
Anyway, linking to my latest in case people find having the formula in a single cell useful. It certainly made my workings more compact and got rid of multiple column/row tables to do the tax calc: Tax rate formulas
