Remaining Filament Estimator

Inspired by this calculator that computes filament based on spool measurements ( https://www.thingiverse.com/thing:1880517 ), this calculator estimates the remaining spool filament length based on weights. It is currently configured to compute based on a 1kg spool.

There is no download in this Thing. The calculator is here: https://jscalc.io/calc/H4YdXILbWRDhOzO0

Required:

* a fresh spool of filament (or, the weight of a full spool obtained from the manufacturer)
* an empty spool of filament (or, the weight of an empty spool obtained from the manufacturer). Yes, there's a Catch 22 here in that you might not have an empty spool to measure. Hatchbox (the brand I'm using) does publish the empty spool weight in their FAQ.
* a digital scale that measures in grams
* knowledge of the number of meters of filament on a fresh spool (obtained from the manufacturer)

There are two constants and one variable:

* **New Spool Weight** -- (constant) the weight (in grams) of a fresh f