This sample is the second grating testing sample from a polished edge underneath and looks like this:

 _____________________
| |                   |
| | ▌▌▌     1         |
| |                   |
| |   ▌▌▌   2         |
|_|___________________|

All gratings are the same frequency. During the Metricon step I damaged the gratings like so:

The Metricon only got a reading off the back sideas follows: