Here's what I would do:
- Measure a sweater or t-shirt that has the length short-sleeve you like. Measure from the top of the sleeve (where it joins the shoulder) down to the "hem". Length B is the measure from the underarm join to the hem.
- Also measure the circumference in two places, a: at the hem and b: just where it joins the underarm. If using a form-fitting t-shirt to measure, add a bit to the circumferences as the sweater will be thicker (maybe add an inch or so for comfort).
- Using your gauge (yes, it's the bane of most knitters but it is also extremely important), cast on the number of stitches necessary to obtain that Circumference A. Increase stitches evenly on both sides of sleeve until you have the length to underarm (Length B) that you want and the Circumference B you want. You can do the math -- how many rows will give me the length I want? How many stitches do I need to increase for CircumB? How often should I increase -- usually you can fudge this a bit: increase one each side every 2 or 4th row depending and then knit even till it's the right length.
- Follow the directions in Budd's book for fitting the sleeve into the sweater -- this is all dependent on the style of body -- did you bind off for the underarm and then decrease a few to make a fitted arm or did you just do a straight armhole with no shaping. This way will work with ANY style sleeve -- raglan, yoke, set-in or square.....
How's that -- clear as mud?