Having given the reader the essential points and short cuts in estimating material, we will now point out what is considerd a source of frequent mistakes, and give a safeguard for it. In estimating material many mistakes are made from omissions. A bill of material for the construction of a building always requires a long list of items, and it frequently happens that some items have been forgotten and left entirely out of consideration. Probably more serious mistakes in estimating material arise from this cause than any other. They are very discouraging to the contractor. They are things he did not count on, but nevertheless he has them to buy, and as extras he always has to pay more for them than he would had he included them in his original bill. Now, if a person had an itemized list of the material entering into the construction of a building, there is no doubt by comparing his bill with the list mistakes from omitting items would be avoided. In a bill there are many items of material that are used for different purposes and different parts of a building, hence to make a list complete in every detail it should mention the part of a building for which each kind of material is used. In the list following, the items which are likely to be used for more than one purpose or part of a building are in full-face type, and the different parts for which the same are likely to be used are in type of the usual face.