MEASURING AND WEIGHING ON SHABBATH AND YOM TOV
42.a. Flour and other commodities which can be added in approximate quantities without adversely affecting the taste of the food should not be measured or weighed on Yom Tov.
42.b. One should not measure or weigh flour, even in order to make certain that one is kneading a dough of a quantity sufficient to require the removal of challa.
42.c. In these cases, the amount of the flour or other ingredients should be estimated.
42.d. 1) It may happen that one has to be precise as to the amount even of commodities such as flour, so as to avoid spoiling the taste of the food.
2) When baking a cake on Yom Tov, this may sometimes be the case.
3) In that event, one may measure these ingredients too, but one should not weigh them on scales.
43.a. All instruments designed for measuring or weighing. such as scales, rulers and tape measures, are muktzeh.
43.b. They may not be moved, except subject to the restrictions applicable to a keli she-melachto le-issur (See Chapter 20, paragraphs 7 to 13.)
