This post list some of the most important numbers which are important for engineers to do back of envelope calculations. This post, I have focussed on seconds. If you hear someone telling that his service gets 1 million hits a day; don't get bogged down with the numbers, it just means he gets 10 requests per second.
Seconds
# Seconds in a day = 86400 (=24*60*60)
= 0.85*10^5
= 10^5
= 0.1 million
# Seconds in a month = 2592000 (=30*86400)
= 2.5*10^6
= 2.5 millions
If an online site gets 10 million hits per day then it means on an average it gets 100 requests/sec.
If an online site gets 10 million hits per month then it means on an average it gets 4 requests/sec.
# Seconds in a year = 31104000 (=12*259200)
= 31 millions
= Pie * 10^7
If we treat a year as 365.25 days then also, # seconds in a year would be 3,155,7600 which would approximate to 31 million.
# Seconds in a century = 3,155,760,000 seconds (considering 1 year = 365.25 days)
= 3.15 billions
Nanocentury is 1 billionth of a century. So, a nanocentry = 3.15 seconds.
i.e. Pie seconds are there in a nano century. This is also known as Duff's Rule.
