These images show the G6 in action on a Sizer (used widely in Coal & Iron Ore mines) and what happens when a low strength washer is used.
The required torque had to be increased by 83% to get the correct tension. The indentation is above 1mm deep.
In this case the client would not have known and the bolts would have broken. This causes massive damage to the machine and causes the site to lose days of production (costing several million dollars).