Rework chemical volume calcs for tiny quantities

[Mike Dewhirst]

With small product volumes and small ingredient proportions, the default mass unit of kilograms is too large to display the chemical volume - due to rounding of all chemical volumes to one decimal place.

Alternatives are: either increase the number of decimal places or user selection of a smaller mass unit for the product volume so rounding to one decimal place makes more sense visually.

My preference is the latter. It is easier to visually understand grams, milligrams and micrograms rather than kilograms with multiple zeros after a decimal point.

This ticket will sit for while waiting for feedback but the likely outcome will be to detect a tiny (rounded to zero) chemical volume when there is an actual product volume and make an automatic suggestion to the user to select a smaller mass unit.

[Mike Dewhirst]

Feedback indicates the commonsense approach is to retain the current behaviour. We will modify help-text to indicate the need to adjust mass units so you get a recognisable value greater than zero.

No-one has asked for the abovementioned auto-suggestion so that will remain on the back burner.

[Mike Dewhirst]

Here is the new text appended to the existing Product volume help text:

Please note that with small volumes and rounding, this value can result in zero chemical volume if the proportion is small. If so, adjust the Product mass units so this value can be larger.