Funny story.. about '10'...
A long time ago back in the mid '80's I used to service amps of all kinds in a workshop I had above the Musicians Pro shop in Brisbane. I had this one dude come in with a faulty Twin Reverb 100W combo and when he came back to pick it up he said he wanted to test it first... I responded "yeah, why not, it's only us in a car park" ... (The car park for the shop was above the store). So we plugged it in, let it warm up, he plugged his guitar in, I wound it to about 3 and he strummed/picked a few notes. All was good. We chatted, talked about what I had done of which one of them was replaced and biased the o/p tubes. We digressed on how he never thought the amp was very loud... I said "Crank it up and we'll see"... foolishly he did, straight up to 10.... He only played a few notes and stopped - a huge grin now firmly etched on his shocked and amazed face.... 10 seconds latter about half the office staff from 2 floors down and Mick the owner of the shop came running up into the car park all yelling "What's going on.??. What's the f^@* was that?" etc.. etc.. etc.. The guitarist dude and I just knowingly smiled and nodded to each other approvingly ...