When 5/8" Isn't 5/8"

I'm still getting used to my nice new sewing machine (not the Pink Singer).  I learned a little something yesterday.

I'm making an apron with a curved seam between the bib and the bottom.  I'd been postponing this part of the sewing, because I didn't feel like doing all that easing.  Turns out that wasn't the hard part.

This being a garment pattern, it called for a 5/8" seam allowance.  No problem - there it is, clearly marked at the top of the throat plate.  Up where the mark is, it looks like I'm not lined up, but that's because this is a curved piece of fabric.  When you look at where the needle is, you can see I'm lined up correctly.

The good news is that the seam came out nice and smooth.  The bad news is the seam allowance measured 1/2".  Huh?

After some analytical thinking, I moved my needle to the left position.  Sewing this way, you'd get your  5/8" seam.  But who's going to sew like that?  Maybe someday I'll understand the purpose of a needle left position.  

I moved the needle back to center position and kept my seam gauge in there.  And then I noticed that the little orange arm was clearly pointing to the white line on the bobbin cover.  So that's the guide I need to use!

I sewed another seam using the newly-found mark.

And now it's just right.  Instead of ripping out that 1/2" seam, I just trimmed right next to it.  That double seam will keep the allowance nice and neat instead of all frayed.