= Minimum incremental motion
<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.<Precision Motion and Positioning: Difference between Micropositioning and Nanopositioning by Physik Instrumente>[Glossary, Design Resolution and Minimum Incremental Motion]{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.
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