What's the use of the tax1, tax2 and tax3 columns

[joebordes]

These columns are used when you set the Tax Mode to Individual. On the top of the inventory lines block there is a picklist to define the tax mode you need, either:

- global, one tax for the whole document, in which case the selected taxes get saved in all the inventory lines with the same values
- individual, where each line has it's own tax settings, in which case each line tax is saved in these columns