TB-500 is usually supplied as a 5 mg or 10 mg vial and reconstituted with bacteriostatic water. Enter your vial size, water and target mcg — the syringe fills to the exact draw.
Reading the result
A 10 mg vial in 3 mL gives ~3333 mcg/mL; a 500 mcg draw is 0.15 mL = 15 units. The cascade shows concentration, mcg per unit and whether it fits your syringe.