Here is a tip for smoother and easier easing for set-in sleeves making use of the different differential settings on a serger -- I do this instead of machine basting to create ease. Before sewing, finish the sleeve cap edge of your sleeve on your serger in the following way: serge with the normal differential setting from the edges to where the easing is. When you get to the easing area (between the notches), change the differential setting to a higher number (experiment on a scrap to see how much differntial you need). Change back to the normal differential setting when you leave the easing area and continue on to the other edge. The higher differential setting gathers the fabric smoothly. While serging, cut as little seam allowance off as possible. There is usually a little bit of fabric left to ease but that's easy to pin in before sewing in the sleeve.