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Vial Bench

Ten small calculators for prepared vials and the barrels they are drawn into, each doing one job.

Barrel reading

A unit is not a volume until you know which barrel. This converts both ways and names the nearest mark actually printed on the one you picked.

Educational arithmetic only. Not medical advice and not a dosing protocol.

Required. The printed numbers mean a different volume on each of these.

Fill the fields in and the answer appears here.

The arithmetic, step by step
  1. units = millilitres × units per mL. The calibration is printed on the barrel: a U-100 carries 100 units to the millilitre, a U-50 carries 50, a U-40 carries 40.
  2. So one volume has three readings and one reading means three volumes. Twenty units is 0.2 mL on a U-100, 0.4 mL on a U-50 and 0.5 mL on a U-40.
  3. The nearest printed mark is the exact figure rounded to the smallest graduation on that barrel, half away from zero. A 1 mL U-100 is normally marked every single unit.
  4. A draw past the barrel capacity is flagged rather than printed as a number the device cannot deliver: 40 units will not fit in a 0.3 mL U-100, whatever the arithmetic says.

Units is the only word in this arithmetic that means nothing on its own

A millilitre is a millilitre everywhere. A unit is a mark on one particular barrel, and the volume behind it is set entirely by how that barrel was calibrated. The same printed 20 is 0.2 mL, 0.4 mL or 0.5 mL depending on what is in the drawer.

U-100 is the most common calibration in most markets, which is exactly what makes assuming it dangerous: the assumption is right often enough to go unchallenged and wrong by a factor of two or two and a half when it fails. Nothing about the answer would look different. That is why the barrel is a required choice here with no default.

What the calibration describes, and what it says nothing about

The calibration is a property of the device and nothing else. A U-100 barrel is marked so that a hundred of its units fill a millilitre. That is the whole content of the number. It carries no information about what is in the syringe, how strong it is, or whether any particular reading is appropriate for anything.

Capacity matters just as much as calibration and is quieter about it. A 0.3 mL U-100 barrel holds thirty units, so any arithmetic that comes out above thirty describes a draw that cannot be taken on it in one go.

Next to this on the bench