microliter

The modern biology bench lives almost entirely inside this unit. A PCR reaction is assembled in 20 or 50 μL, a sequencing library elutes in 30, an enzyme arrives as 1 μL of glycerol stock, and the adjustable micropipette that dispenses them all is the most-handled instrument in the building. For scale, a single drop from a dropper bottle is about 50 μL, a feeding mosquito takes a few microlitres of blood, and the tear film on a human eye is under 10 μL.

Older papers hide the unit behind a Greek letter. Mid-century chemical and clinical literature wrote the microlitre as λ, a bare lambda, so "5 λ of serum" in a 1950s method means 5 μL. The symbol is long obsolete, but the papers still get cited, and the substitution is worth knowing before dismissing a lambda as a wavelength.

The working trap is accuracy at the bottom of the range. An air-displacement pipette within a percent of true at 100 μL can err by several percent at 1 μL, where tip wetting and dead air loom proportionally large, and that error walks straight into every concentration this site's dilution and molarity solvers compute, since $c_1 V_1 = c_2 V_2$ is only as honest as the volumes fed into it.