As anyone who has played backgammon, players can double the value of the game through the use of the doubling cube, 1, 2, 4, 8, 16, 32, 64. Doubling can be used in many contexts. It can be an important tool in understanding exponential processes. The use of the exponential function (the inverse) is another way of looking at these kinds of sequences. So, log(64)=6 because 2**6=64. The base 2 is not usually critical, but using two, makes for a robust measure for noisy processes which are a result of many factors, not only the underlying exponential.
In radioactive decay, one considers the half life number, which is the time it takes for radioactivity to reduce in half, or the quantity of radioactive material to decompose to half its mass.
If one looks at the current corona virus epidemic and postulates that the underlying model is exponential, one can ask the basic question, “What is the half life number?” or in other words, how many days before the number of cases doubles in size.
From a cursory reading of the newspaper headlines, this appears to be about 4-7 days, or about a half week to a week.
30,000…60,000…120,000…240,000…480,000…1million.
That is about 20 days to 42 days, or about one month. This would be the beginning of March, 2020.