sentences:  Since in our case "p"rb, for the same number of counted lines, the base layer lines with a long period advance faster than the revealing layer lines with a short period.At the halfway of the distance "p"m, the base layer lines are ahead the revealing layer lines by a half a period ("p"r/2) of the revealing layer lines, due to which the lines are interleaving, forming a dark moiré band.At the full distance "p"m, the base layer lines are ahead of the revealing layer lines by a full period "p"r, so the lines of the layers again overlap.