I like to do some basic calculations, partly to compare a few companies and determine which is more likely to be a better investment.

Where the numbers fail is when there are non numerical factors invoilved.

As in how do you assign a number to the native issue. It more or less trumps most numbers.

Also while the so called 'market' often applies to all, so company to company works, but it fails if you are estimating sp value relative to 'what it should be'. Again we enter into a realm of subjectivism, so not much help.

Calculations are a good aid in normal times, but they rarely occur.