Viscometers and Viscometry methods are disclosed. In one general aspect a capillary bridge viscometer comprises an input port an output port a first capillary tubing arm in a first hydraulic path between the input port and a first differential detection point, a second capillary tubing arm in a second hydraulic path between the first differential detection point and the output port, a third capillary tubing arm in a third hydraulic path between the input port and a second differential detection point, a fourth capillary tubing arm in a fourth hydraulic path between the second differential detection point and the output port, an adjustable mechanical flow restrictor in one of the first, second, third, and fourth hydraulic paths, wherein the adjustable mechanical flow restrictor is operative to mechanically adjust a resistance to flow of a fluid while the fluid flows through the adjustable mechanical flow restrictor.