A hand-held, electronic multi-channel pipettor comprising: multiple aspiration cylinders, each having a stationary port through which air is aspirated into and out of the respective aspiration cylinder; a plurality of repositionable pipette tip fitting assemblies, wherein each tip fitting assembly has a pipette tip mounting shaft and a cam following pin, each of the respositionable pipette tip fitting assemblies having a lower port for the respective mounting shaft being aligned along a line and having a range of motion along the line; a plurality of flexible tubes, each flexible tube extending essentially from a stationary port for one of the aspiration cylinders to an upper port on one of the repositionable pipette tip fitting assemblies; a handle portion and a lower portion; a first motor in the handle portion for controlling the movement of pistons within the multiple aspiration cylinders; a roller drum in the lower portion that rotates around a drum axis to move the repositionable pipette tip fitting assemblies and adjust the center line spacing between the mounting shafts, the roller drum having individual cam tracks for each cam following pin, wherein the pitch of each cam track is selected so that the center line distance between adjacent pipette tip mounting shafts changes evenly as the roller drum is rotated, each repositionable tip fitting assembly being slidably mounted on at least one guide rod spanning across the lower portion; a second motor located in the lower portion above the roller drum, the second motor having a motor output shaft that rotates around an axis different than the drum axis; wherein torque is transmitted downward from the motor output shaft to the roller drum in order to rotate the roller drum and adjust the centerline spacing between the mounting shafts. multiple aspiration cylinders, each having a stationary port through which air is aspirated into and out of the respective aspiration cylinder; a plurality of repositionable pipette tip fitting assemblies, wherein each tip fitting assembly has a pipette tip mounting shaft and a cam following pin, each of the respositionable pipette tip fitting assemblies having a lower port for the respective mounting shaft being aligned along a line and having a range of motion along the line; a plurality of flexible tubes, each flexible tube extending essentially from a stationary port for one of the aspiration cylinders to an upper port on one of the repositionable pipette tip fitting assemblies; a handle portion and a lower portion; a first motor in the handle portion for controlling the movement of pistons within the multiple aspiration cylinders; a roller drum in the lower portion that rotates around a drum axis to move the repositionable pipette tip fitting assemblies and adjust the center line spacing between the mounting shafts, the roller drum having individual cam tracks for each cam following pin, wherein the pitch of each cam track is selected so that the center line distance between adjacent pipette tip mounting shafts changes evenly as the roller drum is rotated, each repositionable tip fitting assembly being slidably mounted on at least one guide rod spanning across the lower portion; a second motor located in the lower portion above the roller drum, the second motor having a motor output shaft that rotates around an axis different than the drum axis; wherein torque is transmitted downward from the motor output shaft to the roller drum in order to rotate the roller drum and adjust the centerline spacing between the mounting shafts.