I do a lot of chain piecing when I can, and I check the clear plastic plate over the bobbin occasionally. I still manage to "sew air" sometimes, but I'm such a cheapskate that I just keep going until the thread runs out. I'm wondering about the top thread going at a faster rate: isn't that because of the take-up arm pulling each individual stitch snug before going to the next one? It should take a longer length of thread to go around the bobbin mechanism and back to being taut. The stitches should be the same length on the fabric -- at least that what the operation manuals seem to indicate. Or am I in my usual fog?