The format for floating points used in SW is the C
"double" format, which guarantees 15 decimal digits of precision.
the largest and smallest dimensions that can be added and still give a correct result must not have a ratio larger than 1/10E15. If you want to measure nanometers (1E-9 m) and still have some margin for geometric operations, you can't allow dimensions much larger than 1E3 m.
You would think you could "easily" design sub-micron features, especially when setting microns, nanometers or angstroms in the document options,
but it seems the workspace is "fixed" to a few cubic kilometers,
limiting the resolution at the bottom of the scale...
Which limits sketching to 100 nanos while numbers would allow to go down to about 0.2 nanos .
I am not sure if this helps but thought I would give it a go.