U-100 insulin syringes (100 units = 1mL) have minimum measurable increments of 1 unit (0.01mL or 10 microliters). Doses smaller than 0.02mL (2 units) become difficult to measure accurately. For doses below 0.05mL, consider reconstituting to a more dilute concentration to increase injection volume and measurement precision.
Syringe manufacturer specifications detail measurement accuracy limits.