This means that you will naturally work out in one unit but the answer is in a different one. A common example
A patient needs to take Flucloxacillin 250 mg/5 mL as
The total quantity is 200 mL and you should know from practice that the bottles are 100 mL.
In principle, it does not matter what units you are using as long as you are consistent. Doses are normally in mg or mL, but big molecules (such as insulin, some other hormones) are in units.