Step 1: Measuring for Replacements  measuring window
replacements Photo: Russell Kaye The most important step in the
window-replacement process happens long before installation day.
It's when you measure the dimensions of the existing window
frame to make sure you order a replacement unit that’s the right
size . Here's how to do it.  Start by measuring the inside width
of the old window frame, jamb to jamb, in three places: across
the top, middle, and bottom. Write down the smallest of the
three measurements.  Next, measure the frame's height from the
top of the sill to the underside of the head jamb in three
places: at the left jamb, in the middle, and at the right.
Again, record the smallest measurement.  Check the squareness of
the frame by measuring the diagonals from corner to corner. The
two dimensions should be the same. If the frame is out of square
by 1/4 inch or so, don't worry; the replacement can be shimmed
to fit. Anything more may require adjustments to the frame. If
the frame is so out of whack