"Hands up if you have heard the saying "Measure twice; cut once". Now let me introduce one of my own: don't measure; just cut it. There is a reason why one of them is a famous phrase and the other one is just a disaster waiting to happen. I think you know where this is going.. The task was to make a mounting for a power supply. The mistake was thinking that I didn't need to measure it accurately to make it 100% parallel with the motherboard tray already in place."
Check it out over at Bit Tech.