How many significant figures should i state it to?

Question

I am trying to work out the youngs modulus of steel

one of my extension readings is 0.6mm, the rest are to two significant figures such as 2.2mm etc.

To work out the youngs modulus, i have to plot stress vs. strain, and work out the gradient. to calculate strain i have to use this value (0.6mm). Becuase i have used only 1 significant figure in the results for ONE of my plot points, does this mean i can only give the gradient and so the youngs modulus to one significant figure?

Answer 1

In this situation, two significant figures is the correct way to go.

That is because you are looking at the whole body of extension readings in 2 sig figs.  It just so happens that one reading is a small one.

(edit:) Otherwise it would be like saying that a race car only went 1000 ft in a 1/4 mile race, because the first measurement you took was only at the 9 ft mark.

Answer 2

Craigory is wrong. 0.6 is a result quoted to 1 significant figure. Quoted to 2 it would be 0.60. The question is, did you measure it to 2 significant figures?

If you did not then your answer cannot be accurate to more than 1 significant figure. This is because your result cannot distinguish between values between 0.55 and 0.65, that is your end result could be out by as much as 5 parts in 60 or over 8%. Quoting to 2 significant figures implies a maximum error of no more than 1%.