Abstract: A method for the enhanced accuracy in dispensing from a fluid roller dispensing pump, wherein a keyed one way insertable cassette with pump compressible tubing is utilized with the fluid dispensing pump. The cassette holds and maintains a compressible plastic tube adjacent a roller pump, whereby the rollers of the pump compress the tubing to draw and accurately dispense predetermined exact amounts of liquids into vials, hypodermics and the like for accurate medical and/or laboratory use, and wherein slightly improper placement still provides dispensing but with not always detectable inaccuracies. The cassette is provided with positive proper position indicator elements to ensure both proper orientation and complete locking engagement to ensure accurate pumping and dispensing. In a preferred embodiment the pump embodies current use sensors which determine if the cassette, which causes the pump to use more current, is present. A keyed one-way cassette fitting prevents improper placement.