Versum allows you to use a number of usage units for backbar products:

Basic usage unit: 

Regardless of the specific usage unit, every backbar product can also be used with the pack unit. You can use this unit with whole numbers (e.g. 1; 2; 3; etc.) or decimals (e.g. 0.5; 1.5; etc).

Specific usage unit:

If you define a specific usage unit for a backbar product (gram, mililitre, item, ampoule, impulse, unit), it becomes the default unit for that product. However, you can still use the basic unit pack. 

If you add a product and select a specific usage unit, you also need to enter the pack size.