1. Surface stress of the glass can be tested with a surface stress meter by placing carefully the test instrument on the glass surface after applying a few drops of immersion liquid at the bottom of the instrument.

2. Glass bow measurement: A straight thin steel wire is employed as the reference in glass curvature measurement. The curvature of the glass is calculated by measuring the gap between the glass surface and the wire.

3. Glass waviness inspection: Waviness of glass is checked by laying the tempered glass flat, with the blade of a 300 mm straight edge ruler. The ruler is positioned perpendicularly to the direction of the rollers in the glass tempering furnace and closely against the lower surface of the glass. A feeler gauge is used to measure the clearance between the glass and the ruler blade.

4. Glass warpage check: Warpage of glass is checked by laying the tempered glass flat, with a 300 mm straight edge ruler positioned perpendicularly to the direction of the tempering oven rollers and closely against the edge of the glass sheet. The lower surface of the glass is checked by measuring the clearance between the glass and the ruler blade with a feeler gauge. 

5. Visual inspection is used to check roller marks when the tempered glass passing through the inspection lamps mounted on the unloading table.

6. Stress mark inspection: The stress marks on the glass can be detected with a polarizer when tempered glass passing through the inspecting lamps mounted on the unloading table.