ציטאַט אויף ויקרא 15:4

3a) Binyan av vekathuv echad (a general rule implicit in one verse), viz.: "Mishkav" (what is lain upon) is not like "moshav" (what is sat upon [see Vayikra 15]), and moshav is not like mishkav. What is common to them is that they are articles designed for man's (bodily) comfort alone, and a zav (see Vayikra 15:2, Rashi,) defiles them by (their supporting) most of his weight, to (in turn) defile a man by maga (touching) and by massa (carrying), to (in turn) defile clothing. So, (all) articles which are designed for man's (bodily) comfort alone are defiled by a zav, by (supporting) most of his weight to (in turn) defile a man by maga and massa, to (in turn) defile clothing. This excludes (from such defilement) tarkav (a measuring instrument [which was employed for mishkav or moshav]), it being designed for a different purpose (i.e., measuring, and not "man's bodily comfort." (In sum, then, anything designed for man's bodily comfort and used for mishkav is governed by the "one verse" of mishkav, and anything designed for man's bodily comfort and used for moshav is governed by the "one verse" of moshav.)