Maybe you’re short, like me, (have been, all my life!) and need to shorten everything. Or maybe you bought a camp shirt and want to make it straight instead of hanging down in the back and sides.In this case, it was both. This was a crepe shirt (purple, of course) that I wanted to straighten. 
I use a ¼” adhesive tape that dissolves away in the first washing. (26120) It has paper on one side so the adhesive is exposed only on the other side.
I first measure, down the side seams, to be sure that both sides are the same distance from the underarm seam to the current hem. If they are, I put the tape from one side to the other on the back, just above the hem.
Then I go straight across to the front on both sides. I check to be sure this is a good length, and that when I button the shirt, the bottom edges will be even in front. 
I cut off the excess fabric right along the bottom edge of the tape with my favorite Ergo Rotary Cutter (13613 for right handed, 81972 for lefties). The tape serves as a stabilizer for both the cutting and the sewing. Since crepe stretches, this was especially helpful.
Take off several inches of the paper. It’s easy to turn up the fabric against the tape. Then turn it up a second time.
I use a foot with a blade on the right side, set my needle so it’ll sew just inside the fold, lengthen my stitch by half a millimeter, and stitch. Quick and easy!(To find an item or event on our web page after clicking on the teal words, hold down the “Ctrl” key and touch F. Enter the item number in the box, and you’ll be taken to that item.)
You can see what’s new at Erica’s almost every day! Any page of our website has a column on the left that tells you where to find things, and all you have to do is look for “What’s New” in purple, and click to find out.
Oh my gosh, that is so cool. I am going to run over to your site & get some. I too am short & have to shorten everything. That is such a cool way of doing hemming. Thanks for the great explanation.
I'm glad you find it helpful, Rebecca. I see your kitties love fabric, too. Id be happy to include some photos in our Crafter Kitty section of our newsletter. Take a look. http://www.ericas.com/nl/
thats very nice!! thanks for the tips!