0 used when expressing rates, prices, or measurements to mean "for each":
1 for each:
2 used when talking about prices, rates, etc. to mean the amount for each one:
3 according to something:
as per your instructions/letter/request The policy was not terminated as per your request.
It costs a staggering $50,000 per week to keep the museum open to the public.
In China, the policy of one child per family was introduced to stabilize the country's population at 1.6 billion.
The computer screen displays 80 characters per line.
