Table 1.

Summary of the benefits and drawbacks of the three calibration protocols.

Protocol	Benefits	Drawbacks/limitations
Colony-forming units (CFU)	Inexpensive	Lower precision
	Requires no additional reagents	Count affected by cell clumping/adhesion
	Counts only live and active cells, eliminating quiescent cells, dead cells, and debris
	Not affected by cell shape, optics	Labor intensive
		Slow (overnight incubation)
LUDOX/water	Extremely simple, fast, and cheap	Generates only a single calibration point
	High precision	Cell count is still relative
Microsphere serial dilution	Inexpensive	Slightly more difficult to perform, as it must be completed before spheres have time to settle
	Highest precision
	Many dilution levels helps with quality control and corrections
	Also assesses linear range of instrument