Rather than making hems (especially 1/4" or 3/8" ones), I run a basting stitch at the appropriate hem mark using the guide on my machine or my 1/4" foot. I generally use a thread that contrasts with my fabric so it's easily seen.
I then sew the hem with a normal stitch by turning the hem (after finishing it with my seam/overcast stitch) under at the baste line and sewing approximately 1/8" less than the what the baste line was sewn at.
Once I'm done hemming I pull the basting threads. This gives me accuracy and with knits or necklines I find it eliminates stretching problems because I handle the edge a lot less then trying to use a hem guage and pins.