Here's the sleeve schematic:
Here's the sleeve instruction:
This is a real pattern. (As an aside, how do you feel about being told to make two sleeves?) Take note, this is a very simple pattern, four sizes but only two lengths. I've marked in the shaping for all four sizes. The faint smooth red diagonal line is based on the stitch numbers the pattern indicated. On top of that I've overlaid the increase instructions. You can see the instructions follow the line fairly well, however the last straight section varies from seven rows to eighteen rows between sizes. This shaping works well when the sleeve has lots of ease but not so well if it is closer fitting or if you are changing the sleeve length. If you look at your own arm I think most of us would agree the angle of increase is not quite a smooth diagonal. Some of us have arms which are almost the same width from the elbow to the underarm.
Now that you have read this you have a quick and easy way to recalculate if you need to modify the sleeve.