Your crew's at the site and there's a window that doesn't fit the opening. If it can't be made to fit with shims, caulking, and insulation, back it goes to the boneyard, where rejects sit until you find some means to give them away. Accurate measurements and precise ordering avoid that.

Many window replacement companies, such as New York Sash, in Whitesboro, N.Y., have a “measure man,” someone responsible for re-measuring windows after a salesperson has brought in the contract. “The salespeople measure for price,” says Scott Hayes, co-owner of New York Sash. “There's a lot going on [in the sales process], and it's too easy to make mistakes.” But measurement and other errors can still happen, depending on how efficiently the tech performs his job.

A measure tech “can make you profitable, or kill your profitability,” notes Clark Adams, owner of Clark Adams Co., in California. The most common error? Mistaking height for width and vice versa. Well-trained order-entry people can catch that, easily spotting, for instance, the awning window that's higher than it is wide. Here's what also helps:

  • Taking digital photos: Often used in roofing to make sure installers are clear on what needs to be done, and to document the job. New York Sash has salespeople photograph “unique or problematic” situations using (their newly issued) iPads. Installers don't remove a window before verifying that a window of that size is included in the order.
  • Double-checking: For some companies, the most common problem is not windows that were sized wrong but misunderstandings about what was included in the order. Customers, for instance, might have thought they were getting a grille, tempered glass, or something else. You don't want to find that out once the window is in the house.

“The sooner you identify and correct a problem, the less expensive it is to solve it,” Adams says. So a measure tech visit involves not just measuring but checking with customers to ensure that what's about to be ordered is what they believe they bought. And to verify that understanding with a signature on a document.

  • Removing windows one by one: Some installers remove all windows to get started. At Tom's River Door & Window, in New Jersey, owner Bob Mikaelian says the practice is to take old windows out one at a time. It might be easier to remove all at once, but “we don't want to get too far ahead of the process,” Mikaelian says.