had to spend like 15 minutes trying to figure out what the hell a デスケル was. it wasn't in any of the dictionaries i checked!
turns out it's called a "viewfinder" or "compose-it-grid" (a brand name) in english? something you can use to look at a scene and figure out composition for a drawing or painting. i'd never heard of such a thing before.
i think the Japanese name is an abbreviation of デッサンスケール. and probably also a pun on 透ける