Remington Portable with approximate character

A regular, common-as-mud Remington Portable typewriter. It's a century old and of course still works.

It's the #2 variant Portable (as it would be called, after the #3 was introduced). This one had modifications done to the keyboard; the '3'  and the '7' were composited.

The '7' looks like a plus, just like the '4' already has. That is the label-split making it hard to soo, however. The top of the '7' typeslug has been ground flat and a thin sliver of a +/- charatcer soldered on. I.e. it got an around, approximate, just-about type!

The '3' had an equals-sign added, that is a bother to create on a typewriter otherwise so makes perfect sense. The machine however does still have an underscore and a plus, so a +/- could be typed with these two super-imposed (shift-4-6 and then let go of shift). A separate type is of course much neater and sits properly on the baseline.

Now what special use would require basic arithmetic characters as well as an approximate? 

In any case; the only machine I've so far with an approximate character!