Converting the 3D model to Unity3d, if the unit of mm is still maintained, the control of the movement of some objects will be more convenient, and there is no need to switch units back and forth. Take this note so that you can find it after you forget it.
First, set the unit to mm in SW
Tools—>Options—>Document Properties—>Units—>MMGS (millimeters, grams, seconds)
click OK
Generate STEP file (AP214), after importing into 3DSmax
Customize —> Unit Settings —> Metric mm
click OK
post export
Advanced Options—>Units—>Uncheck Automatic, the scene unit is converted to millimeters
then export as fbx
Uncheck convert units in Unity
You can get a model with a unit of 1mm