4?
Explanation:
sorry im not sure but
You can always take a metre ruler as a starting point. Your metre ruler has the same precision as your 15.0cm or 30.0cm ruler, so bring a ruler during exams as they'll come in handy ;)
The order goes like this:
rulers: 0.1cm or 1mm
measuring tape: 0.01cm or 0.1mm
vernier calipers: 0.001cm or 0.01mm
micrometer screw gauge: 0.0001cm or 0.001mm
((if i'm not wrong))
