well I have sanded on a piece of glass in a figure 8 motion and I have grabbed my ruler and put the ruler on it's edge and I have .006 feeler gauge and I cant fit the .006 feeler gauge under the ruler. There are a couple tiny spots where there is still some shiny black as opposed to how the rest of the spacer looks since being sanded.
I figured I would continue to sand in a figure 8 motion until there are no shiny black spots and double check it with the ruler and feeler gauge and if I cant fit the feeler gauge under the ruler then I will consider it flat, at least flatter then it was.
Am I doing this correctly?