uncertainty for birefringence

Howlin

1. The problem statement, all variables and given/known data

I have done the birefringence experiment and need to get an uncertainty for 1/lambda

2. Relevant equations

sinθ/N=n λ
where N is 300000 and n is 1

3. The attempt at a solution

The uncertainity for θ is ±.48nm, (θ is (.5/60)
How do i corralate this uncertanity for an uncertanity for the graph
I have graphed the results on excell and need to know how i get the uncertainty