I need help on a SI unit question.?

Question

I think my teacher worded this awkwardly. If you can help please do.

How does one know how many digits should be in a measurement using a specific measurement tool?

Answer 1

Hes asking how precise your measurments should be with any given tool. The answer is the smallest digit that the tool measures + 1 digit that you eyeball

Answer 2

Your teacher is probably talking about significant figures. in significant figures, you use all the digits you know for certain plus one estimated digit. so in 14.1 centimeters the .1 is the guess, and in 14.0 centimeters, the .0 is the guesss. this is used not only in math but also in chemistry and also physics

Answer 3

This should be determined by the teacher.He/she should say how many digits should be used

Answer 4

This isn't strictly an SI question but applies to any measurement system.

Usual scientific practice is to use half a gradation on the measuring instrument. For example, If you have a ruler with millimeter markings on it, you can read it as being either 1.0mm, 1.5mm, or 2.0mm with no other readings between 1 and 2. Similarly a ruler with centimeter markings you could read off 1.0cm, 1.5cm, or 2.0cm. There is some flexibility in the rules, because a centimeter graduated ruler has pretty wide spaces, you might eyeball 1.0cm, 1.2cm, 1.4cm etc. In this case though you'd be better off with a millimeter ruler if one is available.