floor() design is to round the value down.
ciel() designed to round the value up
round() designed to go to nearest.
so
floor(0.9) = 0
floor(1.8) = 1
floor(0.1 * 20) = 2
floor(0.1) * 20 = 0. Math done in brackets or functions are done first
ciel(0.9) = 1
ciel(1.8) = 2
ciel(0.1) = 1
round(0.9) = 1
round(1.8) = 2
round(0.1) = 0