Mark, I liked having two on my tractor; one for side to side and one for front to rear, and as the previous post shows, you can order then right here on TBN.
After using my tractor on slopes for several years without one, I put one on last year. It basically confirmed my pucker factor calibration. By the tiltmeter, I was not exceeding safe, but I was approaching the boundary. I bought one from the site noted in the post above. Good people to work with. My first one had a design problem. They replaced it very quickly with their improved model.
I also purchased and installed one of the tilt meters on my TC-40D. You may see pictures of it be clicking my signature link. I have two sections on my lot that had very steep slopes and I wanted to see if I would be safe in using the tractor to mow these sections. Turns out that they both exceeded the safe limits so I now mow them both at a 90 degree angle to the grade. /forums/images/graemlins/grin.gif
Without a tilt meter you are just guessing at grade levels. Guessing always seems to get me into trouble /forums/images/graemlins/frown.gif Better be safe than sorry. /forums/images/graemlins/grin.gif
I wouldn't be without one. I mow the back of my dam and when the meter gets near 20, I start down hill. I have seen it go as high as 30 when a wheel drops in a hole and thats scary. At least with my tractor, if I keep it under 20 degrees and go slow I am safe.