Units cannot be selected by a formula but, however, it is possible to introduce rules to select units.
Problem:
Dyes quantities less than 10g must be expressed as a volume of a stock solution at 100% or 10%.
Solution:
As formulas cannot be introduced to select a unit, we will introduce in the dye operation two dyes lines, one with a unit expressed as a volume and the other with a unit expressed as a weight.
To avoid from displaying twice a dye (one time for each unit), we will introduce a formula that sets quantity to zero when the unit is the wrong one. As the dyes quantities should not be definitively modified by these formulas, formulas will be set as ‘display only’.
See attached document.