How Do I Express the Spring Constant with Significant Figures?

[mircobot]

I know this seem pretty ridiculous to ask to such a large forum, but for my physics lab I have found a spring constant to have a value of 0.1368 N/cm with an uncertainty of 5x10^-4. How do I express the spring constant?

So far I think it is (13.68 +/- 0.05)x10^-2 N/cm but the scientific notation is wrong on the 0.1368 value.

Also, on a side note. For my lab I made a graph Force vs Delta X of Spring. We used a nylon sheath and put mass on the end of it and recorded the distance stretched. The graph shows two linear relationships. One linear slope that starts up with a very small slop, and then suddenly jerks to the right to another linear relationship with a larger slope. My professor has already told me that it has nothing to do with the yield or ultimate strength of the nylon sheath. Any ideas to help me out?

Thanks for your time.

 

[EricVT]

I don't think there is anything wrong with simply writing k = 0.1368 +/- .0005 N/cm. That's how I would personally write it, but I know how labs can be pretty strict on these sorts of procedures.

 

[mgb_phys]

probably 1.368 (+/- 0.005)x10^-1 but i would prefer evict's as clearer