The U-40, 1 mL barrel
40 units to the millilitre, 40 units of capacity, marked every 1 unit. Everything below is computed from those three figures.
Educational arithmetic only. Not medical advice and not a dosing protocol.
| Property | Value |
|---|---|
| Units to the millilitre | 40 |
| Capacity | 1 mL, which is 40 units |
| Smallest printed mark | 1 unit, which is 25.0 microlitres |
| Half a mark | 12.5 microlitres |
What is particular to this barrel
Forty units to the millilitre. Every printed number means two and a half times the volume it would mean on a U-100, which is the largest discrepancy of the five and the reason the barrel selector on every tool here starts empty. A reading of 20 is 0.2 mL on a U-100 and 0.5 mL here: the same number, two and a half times the liquid.
Forty marks over a full millilitre, so each graduation is 0.025 mL. The coarsest of the five, and the one where rounding to the nearest mark costs the most.
| Reading, units | Volume, mL | Volume, microlitres | Half a mark, as % of the draw |
|---|---|---|---|
| 2.0 | 0.050 | 50 | 25.00% |
| 4.0 | 0.100 | 100 | 12.50% |
| 8.0 | 0.200 | 200 | 6.25% |
| 12.0 | 0.300 | 300 | 4.17% |
| 16.0 | 0.400 | 400 | 3.13% |
| 20.0 | 0.500 | 500 | 2.50% |
| 28.0 | 0.700 | 700 | 1.79% |
| 32.0 | 0.800 | 800 | 1.56% |
| 36.0 | 0.900 | 900 | 1.39% |
| 40.0 | 1.000 | 1000 | 1.25% |
Where the reading error stops being ignorable
Half a graduation on this barrel is 12.5 microlitres, and that figure does not change with the size of the draw. As a share of the draw it therefore grows as the draw shrinks: at 2 units it is 25.0%, and it keeps climbing from there.
Below two graduations every tool on this bench flags the reading rather than printing it plainly, because at that point the uncertainty in the measurement is a large fraction of what is being measured and the precision of the arithmetic has stopped meaning anything. The fix is not a better calculation. It is more liquid, which is what thinning a solution is for.
| Printed reading | U-100, 1 mL | U-100, 0.5 mL | U-100, 0.3 mL | U-50, 0.5 mL | U-40, 1 mL |
|---|---|---|---|---|---|
| 5 units | 0.050 mL | 0.050 mL | 0.050 mL | 0.100 mL | 0.125 mL |
| 10 units | 0.100 mL | 0.100 mL | 0.100 mL | 0.200 mL | 0.250 mL |
| 20 units | 0.200 mL | 0.200 mL | 0.200 mL | 0.400 mL | 0.500 mL |
| 30 units | 0.300 mL | 0.300 mL | 0.300 mL | past the barrel | 0.750 mL |
| 40 units | 0.400 mL | 0.400 mL | past the barrel | past the barrel | 1.000 mL |
| 50 units | 0.500 mL | 0.500 mL | past the barrel | past the barrel | past the barrel |
What this page is not saying
Everything here is a property of a manufactured object: how it is marked, how much it holds, and what follows arithmetically from those two facts. Nothing on this page says which barrel anybody should use, what should go in it, or what any reading on it should be. A calibration is a measuring scale, and a measuring scale has no opinion about what is measured with it.
Next to this on the bench
- The barrel reading tool
This barrel, any volume, either direction.
- The other four barrels
Same treatment, different three numbers.
- Rounding to the nearest mark
The reading-error arithmetic in full.