The body of the Riverstone gauge---they actually make two, but get the one with the extension arm which puts the stylus at playing height when measuring VTF---is made of a tough plastic, and that extension arm of a non-ferromagnetic grade of stainless steel. The gauge has resolution to 0.005g (!), and can be recalibrated to zero via the 5 and 20 gram weights included. Riverstone Audio has a video on You Tube in which the gauge is displayed, described, and explained, and then demonstrated.
The ubiquitous electronic gauge that most companies are rebranding and marketing as their own is, in comparison, a piece of junk, regardless of price. Many of them sell for more than the Riverstone, some much more. I mean come on, $28.95---whaddaya got ta lose?! For more details, see the Riverstone Audio website.