Daniel, that's the exposure compensation button. That's the right one. I wouldn't worry too much about the background blowing out, the knife is the subject and what you want to expose properly. Also, you can take a quick look at the settings when in P mode, then switch over to manual and set it to keep your settings the same. You are basically using your camera in P mode as a light meter.
Play around. In manual mode it's easy to see what each setting does. Bigger aperture (smaller number, just like fractions) more light so to compensate you go to a faster shutter, etc...
I need to order several bow strings soon, two for each bow. I'm going to switch my other recurve back to traditional Flemish twist string and have a spare. Breaking one in the field is no fun. Oh, I could use a new arm guard, would Momma Fairly be up for a leather working project?
-X