An oven: Its beginning is four [handbreadths] and its remnants are four [handbreadths, these are] the words of R’ Meir. But the Sages say: When do these words apply? In [the case of] a large [oven], but in [the case of] a small [oven], its beginning is the smallest amount and its remnants are the majority of it. [The above applies] from the time its manufacture is complete. What is [considered] the completion of its manufacture? From when one heats it enough to bake sponge cakes in it. R’ Yehudah says: When one heats a new [oven] enough to bake sponge cakes in an old [oven].