Danshi yana nufin adadin tururin ruwa a cikin iska. Idan ana ruwan sama, iska tana da danshi sosai saboda tana ɗauke da tururin ruwa mai yawa. Akasin haka, idan iskar ba ta ɗauke da tururin ruwa sosai ko babu, iskar ta bushe sosai. Ana bayyana adadin tururin ruwa a cikin iska a matsayin ɗan danshi.
Danshin da ke da alaƙa da juna shine rabon matsin lamba na tururi da matsin lamba mai cike da tururi na ruwa a wani zafin jiki (ta tururi a nan muna nufin tururin ruwa). Danshin da ke da alaƙa da juna ana bayyana shi a matsayin kashi, wanda aka tsara shi ta hanyar lissafi kamar haka:
Akwai wata sabuwar kalma, wato matsin lamba na ɓangare. Matsi na ɓangare shine matsin lambar da kowace iskar gas ke yi a cikin iska. Iska a zahiri ta ƙunshi nau'ikan iskar gas daban-daban... akwai nitrogen (78%), oxygen (21%), argon (0,90%), carbon dioxide, tururin ruwa, da sauransu. Jimlar matsin lambar kowane iskar gas a cikin iska ana kiranta jimlar matsin lamba (jimlar matsin lamba = matsin lamba na yanayi = matsin lamba na iska). Idan babu abun ciki na tururin ruwa a cikin iska, to matsin lambar tururin ruwa = 0. Akasin haka, matsin lambar tururin ruwa ya fi yawa idan matsin lambar tururin ruwa = matsin lamba na tururin ruwa mai cike da ruwa. Matsin lambar tururin ruwa mai cike da ruwa ya dogara da zafin jiki (duba tebur da ke sama).
Idan matsin lamba na tururin ruwa ya ragu = matsin lamba na tururin ruwa (danshi mai dangantaka = 100%), to iskar ta cika da tururin ruwa… Lokacin da iskar ta cika da tururin ruwa, adadin tururin ruwa a cikin iska ya kusa kaiwa ga matsakaicin ƙimarsa… Idan matsin lamba na tururin ruwa ya ragu > matsin lamba na tururin ruwa (danshi mai dangantaka > 100%), to iskar ta cika… Lokacin da iskar ta cika, iskar ba za ta iya riƙe adadin tururin ruwa ba… Domin iskar ba ta iya riƙe adadin tururin ruwa ba, yawan tururin ruwa zai koma ruwa (karanta: raɓa)... Zafin da tururin ruwa ke taruwa zuwa raɓa ana kiransa da wurin raɓa.
