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Design resolution is the theoretical smallest commanded movement implied by a positioning mechanism's drive components. For a screw drive, it can be calculated from screw pitch, reduction gearing and motor or encoder increments. It is not automatically the minimum incremental motion that the final load executes repeatedly.^[ref]

For an original ideal drive, let a lead screw advance $p=0.50\mathrm{mm}$ per revolution, with 50 motor revolutions per screw revolution and 2000 resolved counts per motor revolution. One count corresponds toDoubling the count resolution to 4000 per motor revolution gives theoretical $q=2.5\mathrm{nm}$ without changing the screw. That calculation does not halve friction or remove backlash. A controller may display both increments even if the load moves only after several such commands have accumulated.

Keep the location and counting convention of the feedback sensor explicit. Counts at a motor shaft, counts at a screw and directly measured load position are different observations. A gearbox can introduce compliance between them. Pair the design calculation with an independent motion test to establish operational performance. A smaller theoretical increment also does not by itself establish absolute positioning accuracy or a smaller measurement uncertainty.

Minimum incremental motion is the smallest displacement increment that a positioning system can execute repeatedly for the specified input and test conditions. It is an operational motion property, whereas design resolution is derived from the drive geometry and electronic increments. Friction, stiction, elasticity and backlash can make them differ.^[ref]

For an original illustrative test, independently measure the displacement produced by repeated commands from equivalent starting conditions. A nominal 10 nm command gives moves $0,20,0,20\mathrm{nm}$. Their mean is 10 nm, but that mean does not show repeatable 10 nm increments. A nominal 40 nm command instead gives $39,41,40,40\mathrm{nm}$.

Define an example acceptance rule before testing: every measured move must lie within 5 nm of the command, and the readout must have sufficiently smaller uncertainty, stipulated here as 1 nm standard uncertainty. The 10 nm trials fail this rule; the 40 nm trials pass. Among these two candidate increments, 40 nm is the smallest accepted one. It is not a proof of the globally smallest achievable increment because intermediate candidates and other conditions were not tested.

Report the command convention, load, motion direction, starting procedure, displacement sensor, measurement uncertainty and acceptance rule. A rotary encoder on the motor does not automatically measure the final load motion. Independent readout, for example with an interferometer, tests the assembled stage rather than only the commanded count. Positioning repeatability at a target and the ability to make a small move are related but distinct properties.

Physik Instrumente makes precision motion equipment used in scientific apparatus. Its archived M-222–M-226 motorized micrometer family illustrates a concrete measurement issue: motor-shaft encoder counts and screw geometry give a design resolution, while actual motion also depends on mechanics and loading.^[ref]

For a worked reconstruction from the manufacturer's M-222.20 specifications, use screw pitch $p=0.5\mathrm{mm}$ per revolution, gear reduction $G=(31/9{)}^4$ and 60 encoder counts per motor revolution. The nominal linear increment isThis agrees with the listed design resolution of $0.059\mu \mathrm{m}$. The same table separately lists minimum incremental motion of $0.1\mu \mathrm{m}$ and backlash of $5\mu \mathrm{m}$ for that model.^[ref]

Thus a command corresponding to one encoder count is not evidence for an independently resolved 59 nm movement of the load. The listed backlash corresponds to roughly 84 nominal counts, illustrating why reversing direction is a different test from continuing in one direction. These are calculations from a legacy specification, not new performance measurements. In an assembled instrument, compare commanded and independently measured displacement, including reversals, to establish the usable response and its measurement uncertainty.