Improve precision of float numbers

[Chasfield]

As an aside:

You could consider some other Arduino related development boards.

The The PJRC Teensy 3.2 board will do 64 bit maths out of the box and can be programmed from the Arduino IDE once Teensy extensions have been added.

The ageing Arduino Due will do the same job, but its form factor is somewhat bulky for home-made calculators.

Both of these options remove the resource ceiling of the 8-bit Arduino family. You are left wondering what code you can add to fill the device up instead of scratching around to save a few bites of RAM or heap space.