What does tighten an additional 55 degrees mean?

:shakehead 97 chevy silverado cylinder heads. Tightening sequence says tighten all to 22 lbs the tighten the short bolts an additional 55 degrees, the med ones 65 degrees and the long 75 degrees. How much of a turn is that?

A full turn is 360, half turn is 180, 1/4 is 90, and 1/8 turn is 45 degrees. So, just a bit over 1/8 of a turn. But, I've never seen things referenced like this. Where did this come from?

What engine?
When turning in degrees they make a tool with the degree reading wheel on it.
Check your local parts place tool store or a auto tool dealer.
Are you using new head bolts?
And double check your specs on it.