mm is correct, The correct method is to push a caulk gun, not pull it.

By using masking tape as a border, as previously mentioned, is also
another good idea, provided you haven't laid a ton of caulk into the
joint/seam. Otherwise, as you pull the tape right after caulking, you
will not get a clean, or proper seam.

I've seen recently rolls of Silicone Caulk Tape sold in Stores like Home
Depot, and Lowes, which comes in different widths, is made for caulking
around bath tubs, and the backing is peeled off, and the tape applied.
Sounds like a good idea, but I have never used the product to comment on
how well it works. Mark