I know that there are a lot of TechCheck gizmos out there! But I Would like to share with all of you my version, which I find very handy and simple to use. In the beginning, it started as a gizmo version of the TechCheck Script from Josh Parks, but the gizmo evolve 'a lot' through the time (just to make it easier for me to use it and adding some funcionalities) and I think that it can be useful to everybody.
Checking Steps: White Levels, Black Levels, Saturation, Grain, Nan/If pixels, negative Pixels, Difference...
Check Against Plate: Compare any of the steps against the original plate!
Contact Sheet: Choose between a simple view or a contact sheet with 4 layers (rgb/luma, r, g, b)
Alerts: activate alerts about Bbox, format and frame range.
Download it from Nukepedia! http://www.nukepedia.com/gizmos/other/mttechcheck