# Help sig figs in experiments

1. Mar 17, 2013

### physicsbanana

Hello,

I am having trouble with significant figuress in experiments! Thanks for any help you provide!

I have an experiment where I pick the mass, and I chose 200g. So if I want to convert this to mks units i would do the following:

200g x (1kg/1000g) = 0.2kg

Is this calculation correct/valid? Then my mass will have one sig fig because of the 200g value.

Thanks

2. Mar 17, 2013

### haruspex

You need start by knowing how accurate the 200g is. If it's accurate to within +/- .005g then it's 200.00g; if it's only accurate to the nearest 5g then it's 2.0 102g. Once you have that right, expressing in kg is easy.

3. Mar 17, 2013

### physicsbanana

That's what i don't get...I picked a 200g mass and used it

How do I known how many significant digits if it was not a given value?

I used a 200g metal mass that was labeled "200g". Isn't this number perfect?

4. Mar 17, 2013

### haruspex

Nothing in the macroscopic real world is exact. The set of masses should come with some statement regarding their accuracy. If not, weigh it on the most accurate balance you have and use the known accuracy of the balance.