But do give an O(x) feel for how expensive operations are.

Back-of-the-envelope calculation: how many piano tuners in Sydney?

• Sydney has ≅ 4 000 000 people
• Average household size ≅ 3 ∴ 1 300 000 households
• Lets say that 1 in 10 households owns a piano
• Therefore there are ≅ 130 000 pianos
• Say people get their piano tuned every 2 years (on average)
• Say a tuner can do 2/day, 250 working-days/year
• Therefore 1 tuner can do 500 pianos per year
• Therefore Sydney would need ≅ 130000/2/500 = 130 tuners