**Too difficult**

Some calculations are extraordinarily hard to do accurately, even though they often appear simple at a glance or quick thought. When you start to go deep down into them, you find a lot of details that quickly make your life a misery. Calctool calculations are generated from "a little bit of Javascript", not a mountain of programming. Differential equations and the like are out for me!

Into this category fall items such as Mie scattering, the Chinese calendar, and sextant sight reduction calculations.

**Numerical solutions**

Calculations that require numerical integration or large lookup tables to perform are also too much hard work to program (unless some kind benefactor could donate Javascript). Sorry, but no integration of probability distributions, or estimation of the three-body problem, in the near-future.

**Mind-numbing for my advanced years**

In the past, in my young mathematical prime, I could derive equations for anything you could care to mention. Recently however, I have been stumped by some worryingly trivial problems. That's why, for example, there's no calc for the elastic collision of spheres.

**Too much like programming**

I'm no programmer, so even some simple calculations are outside my ability. Things that I'm sure are easy, like the manipulation of times and dates, and having textual inputs and outputs, are largely down to other volunteers to produce.