For example on day 1 I ran 3 samples, on day 2 I ran 3 samples, on day 3 I ran 9 samples, on day 4 I ran 6 samples, etc.

I have calculated the standard deviation for each individual day on each instrument. For example I have the standard deviation between the three samples run on day 1 on instrument 1, and also have the standard deviation between the three samples run on day 1 on instrument 2.

Now I would like to combine the standard deviations from each day to get an average to compare the standard deviation from instrument 1 samples to the average standard deviation for instrument 2 samples.

I have basically no experience in statistics. Can anybody point me in the right direction to accomplish this?

Thank you!