A window sill was placed in the room. While measuring for a corner window with a shelf, find the measuring point.
Left-hand recess should be starting.
Move a piece of string along your window shelf to the opposite window pane of the left-hand recess.
Now start from the right-hand recess
Cross-check the measuring point
Measurements for an inside Z- Frame
Start with separating corner windows into parts that are Right Corner Window R and Left Corner Window L. From the left corner window, start the measuring process. Z- Frame templates can make the procedure easy.