> we can't have more than 2 numbers visible after the decimal point on the tool barre?

You can have more - go to Options and set "Decimal places to display" to a different number, just the default is 2.

But several things such as intersections are calculated to a precision of 0.001 units. So unless you stay away from operations that involve tolerance (Boolean, Intersections, Fillets, Offsets, ...), it probably won't do you too much good to look at many more decimal points in the UI.

You generally need to pick a proper unit system and scale for your object such 0.001 units is smaller than the smallest detail that you want to represent, and your object should generally be less than 5000 units in overall size, otherwise there will tend to be problems in areas that require complex mathematical calculations such as Booleans and Fillets.

- Michael