We have this relation between centimeter and millimeter.
1 cm = 10mm
So out of the two millimeter is smaller unit of measurement.
Smaller the unit, more precise is the answer.
Like for example , if we want to measure size of an ant which is approximately 5mm, so in that case cm scale can only give values for 1 cm or 2 cm but not exactly 5mm. Only mm scale will give accurate answer.
So we can say millimeter will give Lauren more precise answer.