We use a set automated vacuum syringe to pull the correct quantity of oil into the auto filler prior to it being inserted into the 10ml vial for filling. The gauges are set and secured at the start of each filling run and signed off by the production line QA officer prior to a production run. Please be aware that the vials we use for injectables can hold up to 12ml of oil making it look like its under-filled because it leaves a space at the top of the vial however, all vials are filled with a minimum of 10ml.
A simple way for you too check the vial amount is to insert a 10ml syringe into the vial and suck out all the oil to confirm its unto or past the 10ml mark. Don’t remove the needle from the vial when you have done this simply push the oil back into the vial when your satisfied the amount is correct. When drawing out weekly injection amounts, make sure you extract exact quantity every time. Failure to correctly fill the syringe to the intended amount will result in you having more or less oil at a given point in your cycle than you originally accounted for. If you over filled the syringe each time even by 0.1ml after 10 withdrawals you will be 1ml short of what you planned and that's where the confusion starts with vial fill levels.