They had to replace the apron and stool on the window because they were too short. He had to chisel away the stool on the inside because it went all the way to the outside and replacing the whole thing would mean taking out and reinstalling the whole window. He set a scribe to the distance between the casing and the edge of the stool and marked that same distance from the side of the casing to get the length of the stool. He put in wooden jambs since it was only plaster around the window. He did not build the jamb into the window opening, he built it separately on sawhorses and installed the casing on it there as well. He then installed the whole assembly into the window opening as one unit with nails and screws. He had to break some of the plaster that was causing a gap. He then cut an apron with a length of the distance to the outside of the casings on each side and nailed it in place.