Hi Javier,
Three digits are to my knowledge what is set as input option, no change.
If you work, for example in cm, go to the Preferences>Units and set it to mm. This will give you also three digits on the right, but it equals four compared to cm.
Another way would be to work on a completely different scale. Attribute Manager> Mode> Project> Project settings.
https://help.maxon.net/us/#DDOC-DOCUMENT_GROUP_PROJECTSETTINGS
The whole project can be scaled at once.
During data entry, you can even specify the units directly, each time exactly what you need.
https://help.maxon.net/us/#PREFSUNITS-PREF_UNITS_MAIN_GROUP
The option Auto Convert should be on, changing it might require a restart. In r20 though, I found it malfunctioning.
Perhaps even 100 times the scale is way more appropriate if such precision is needed. Of course left sided digits shouldn’t be extreme as well.
All the best