This is Part 7 of 8 of the double hung Andersen replacement window installation series.
The exterior stop cover is provided with each window come pre-cut two inches in width and rough cut to the length of each window they will need to be ripped to width and finish cut to length for each window begin at the top of the window and measure the length from side Jam casing to side gem casing next measure between the exterior casing and the trim curve on the insert
window for the width use a miter saw to cut the top cover to the length you just measured but don't cut it all off one end remove an equal amount of material from each end to achieve the proper length this will maintain the proper profile for installation into the kerf on the window use a table saw to rip the exterior stop cover to the proper width line up the exterior stop cover at
each side and press and snap into the kerf in the window next measure the length of both side exterior stop covers measure from the sill to the edge of the exterior stop cover you just installed subtract one sixteenth of an inch from this measurement to allow for drainage at the bottom take a measurement between the exterior casing and the trim curve at each side for width cut both pieces to length with a miter
saw make certain to make the cuts at the top end of the stop covers then rip both pieces to width with the table saw line up the top end of the piece tied to the top exterior stop cover and press and snap into place make certain you maintain the one sixteenth inch gap at the bottom to allow...
See more here: https://www.youtube.com/watch?v=YTLN_Zc_kOM