How is the reading time computed?
The way the reading time is computed is quite easy. It follows this formula
$$ \frac{\text{Number of words in the post}}{\text{Average reading speed in words / min}} $$
The average reading speed for college students is assumed to be 300 words per minute, according to this page, for normal text. If there are formulas and new concepts I use 100 words per minute. When the post is very short, the time is simply $<1$ less than one minute, like this one. Also, the words are counted by copying the whole raw text with html tags into this page, and the result is rounded up so it may be bigger than expected.