spec says -0 30'

does that mean half a degree neg?

thanks

 

Yes, that's half a degree.

Angles are often measured in degrees, minutes, and seconds. It dates back to the days of seafaring exploration (think Cap'n Cook, Columbus, Magellan, etc). Obviously you still have 360 degrees to a circle, but you have 60 minutes to a degree, and 60 seconds to a degree. 30' is thirty minutes = 30 minutes out of 60 minutes = 1/2 = 0.5.