Using Costco's Photo Lab

I like to use the Costco Lab for proofing or quick prints, but I like to do my own image corrections. It is not uncommon for the lab to forget and run their corrections anyway. The staff are usually very pleasant about it and they re-print my files right away, but it is an inconvenience. From talking to the staff at some of the different Costco Warehouses in my area, I have learned a few things which I thought I might share with you.

The above image shows what the code on the back of the photo should look like if the lab turned their image correction off. You only need to worry about the part I marked in red.
The sequence code should be:
N N N N---
(four n's and a set of three dashes)

If their image correction was on at the time of printing, the sequence will be:
N N N N NN
(four n's followed by a double n)

I hope this was helpful.