Which increase to use?

I’m making scarlettknits lacy mock cable socks, found here http://www.ravelry.com/patterns/library/lacy-mock-cable-socks. The directions for the gusset call for increasing 1, but do not say which increase to use. Any help will be appreciated. :shrug: :shrug:

I think I’d do a M1 purl. It doesn’t look like it should be a decorative increase.

Is this the same as M1F as shown on Amy’s video?

That looks like it’s on the knit side. What I do for a purl increase is to lift the bar with the left tip from back to front and then purl into the front loop.