1. There is a dispute about whether one is allowed to weigh food on Yom Tov.
2. The Chachamim say that one is not even allowed to put food on a scale in order to save it from being eaten by mice (if left on the floor).
3. A chef may not weigh food even without a scale.
4. There is a dispute about whether one should show his Shechitah knife to a Chacham on Yom Tov for examination.
5. One is not allowed to straighten a spit on Yom Tov.
A BIT MORE
1. Rebbi Yehudah: One may not weigh food with a scale, but he may weigh it opposite a vessel and then weigh the vessel after Yom Tov. Chachamim: One may not use a scale at all on Yom Tov.
2. This is prohibited as long as it merely looks like one is using the scale to weigh the food. In contrast, one may store food in a scale that is clearly not being used as a scale, such as a scale that is not hanging on the rope from which it normally hangs when it is used to weigh things.
3. For example, he may not weigh food with his hand. Similarly, he may not put meat into a cup of water that has markers indicating how much the water rises when the meat is put into it.
4. The Rabanan say that he should not do so, lest the Chacham tell him that his knife requires sharpening, which might lead him to sharpen it.
5. Since it is usable for roasting meat even if it is not straight, it is considered an unnecessary task for food preparation on Yom Tov.