Do you have the same stitch gauge as the pattern? Figure out how many inches the pattern gauge is over 52 sts and measure your sleeve to see if it's the same. If yours measures more, then you can decrease again until you get to the same measurement, then knit straight. If you do, then just knit straight. Most arms are pretty much the same diameter from wrist to elbow and 10" sounds like that would cover it. If you do want a more tapered lower sleeve, you can dec a few more sts every 2-3".
sue- knitting heretic