astGrad VS numbat

I mean that article of yours highlights the difficulties one encounters fairly well, I would say. I don't disagree that this is (generally) a tricky problem!

Nim allows you to do a lot, e.g. derivatives of a unitful expression with measurement errors [0]. But other aspects run into the reality of dealing with a static type system. For example in Measuremancer [1], the library handling measurements with uncertainties, each `Measurement` is a single generic `Measurement[T]`. Each measurement stores the derivatives for error propagation. Obviously the derivatives have different units. Now, we could make `Measurement` a two-fold generic, `Measurement[T, U]`, but that just makes things more unwieldy in practice, for not much gain.

Without rewriting a majority of existing code you will always run into trouble where your perfect unit type system will either break or you'll need to work around it anyway (e.g. calling into some C library for part of the code).

[0]: https://github.com/SciNim/astGrad#extra-fun

[1]: https://github.com/SciNim/Measuremancer/

> 365·243 ought to be 365·2425 exactly:

Yes. This is also how it is defined: https://github.com/sharkdp/numbat/blob/ba9e97b1fbf6353d24695...

The calculation above is showing a rounded result (6 significant digits by default).