Hair grows at a pretty constant rate, but when it's very short the growth looks more because it's proportionately more.Hair takes about three days to grow a millimetre. Suppose you start with it shaved down to the skin. Then:After three days it has grown from 0 to 1 mm. That's a large change, quite noticeable.After another three days it has grown from 1 to 2 mm - so the amount of hair has doubled, an increase of 100%.After another three days it has grown from 2 to 3 mm - that's an increase of only 50%.After another three days it has grown from 3 to 4 mm - an increase of 33%.After another three days it has grown from 4 to 5 mm - an increase of 25%.And so on. Soon the increase over three days becomes not noticeable, and it seems that growth has slowed down.