using the AutoCad Companion 2008 Book and had a question to get answered ASAP for fin

Hey everyone, this might be a dumb question but I'm working chapter 9 on the GasketA project and I was wondering if any has used this book and knows what the small circle with the line through it means radius or diameter, it seems its radius when i draw things, but the symbol seems more like a diameter look to me. Also, by the illustration it says 4X R0.50, what does this mean?

The circle with the line = Diameter

Radius is signified with the letter "R"

4X R0.50 = 4 arcs each with a radius of 0.5

thank you so much! now i can continue with this plaguing assignment haha