This is a calculation to check glass. The stress on the glass is correctly calculated to be 152.8 MPa ( 22,000 psi), but the engineer says "O.K." because he uses an allowable stress of 750 MPa (108,700 psi) for the glass. That's over four times the allowable stress for STEEL.

Had he checked deflection, the 810 mm (31.8 ") deflection might have tipped him off that there was a problem. But then again, the 3.8 metre (12.5 ft.) simple span didn't ring any bells, so maybe not.