A pipette calibration and volume offset mechanism for a pipette to which the mechanism is to be installed, the pipette being configured to aspirate a volume of a liquid of interest simultaneous to an axial return motion of a piston of the pipette from a lower stop position being a home position to an upper stop position along an upward direction which is a distal-to-proximal direction, the mechanism comprising: a housing; a mode selection mechanism having a mode selector element movable between a first and second position, the mode selection mechanism being axially and rotationally constrained at a proximal end of the housing; an axially displaceable follower element interposed between the mode selection mechanism and the housing and coupled to the mode selection mechanism characterized in that the pipette calibration and volume offset mechanism further comprises: an offset counter located within the housing and axially movable with the follower element; a threaded element located within the housing and having an axial position that is adjustable to define the home position of a pipette to which the calibration and volume offset mechanism is installed; a coupling located within the housing, the coupling rotationally coupled to the threaded element and operative to selectively rotationally couple the offset counter to or decouple the offset counter from the threaded element; and a user rotatable input mechanism that is rotationally coupled to the coupling; wherein, the offset counter will not rotate with the input mechanism and the coupling when the mode selector element of the mode selection mechanism is in the first position; and wherein, the offset counter will rotate with the input mechanism and the coupling when the mode selector element of the mode selection mechanism is in the second position. a housing; a mode selection mechanism having a mode selector element movable between a first and second position, the mode selection mechanism being axially and rotationally constrained at a proximal end of the housing; an axially displaceable follower element interposed between the mode selection mechanism and the housing and coupled to the mode selection mechanism characterized in that the pipette calibration and volume offset mechanism further comprises: an offset counter located within the housing and axially movable with the follower element; a threaded element located within the housing and having an axial position that is adjustable to define the home position of a pipette to which the calibration and volume offset mechanism is installed; a coupling located within the housing, the coupling rotationally coupled to the threaded element and operative to selectively rotationally couple the offset counter to or decouple the offset counter from the threaded element; and a user rotatable input mechanism that is rotationally coupled to the coupling; wherein, the offset counter will not rotate with the input mechanism and the coupling when the mode selector element of the mode selection mechanism is in the first position; and wherein, the offset counter will rotate with the input mechanism and the coupling when the mode selector element of the mode selection mechanism is in the second position. an offset counter located within the housing and axially movable with the follower element; a threaded element located within the housing and having an axial position that is adjustable to define the home position of a pipette to which the calibration and volume offset mechanism is installed; a coupling located within the housing, the coupling rotationally coupled to the threaded element and operative to selectively rotationally couple the offset counter to or decouple the offset counter from the threaded element; and a user rotatable input mechanism that is rotationally coupled to the coupling; wherein, the offset counter will not rotate with the input mechanism and the coupling when the mode selector element of the mode selection mechanism is in the first position; and wherein, the offset counter will rotate with the input mechanism and the coupling when the mode selector element of the mode selection mechanism is in the second position.