 So before then, the schoolrooms were filled with this dust that went everywhere. I mean, if you were ever in a schoolroom that had a chalkboard, if your experience was, your chore was to beat the, clean the dusty chalk erasers at the end of the day, you would know that quite a lot of dust comes from the chalkboard. In any case, so by 1902, they invented this kind of dustless chalk that was incredibly successful, and teachers loved it.