The original Linn's Multi-Gauge (blue envelope, stiff plastic) was even farther from true than the Instanta. The late Stuart Morrissey sold the entire batch in China to recover his costs while keeping them off the U.S. market. The corrected Linn's Multi-Gauge (red-brown envelope, flexible film) is accurate for your purpose.

The original Linn's gauge was recalled based on a reported error of 0.04 (at gauge 8.29) to 0.08 gauge (at gauges 9.97 to 11.93) plus a parallax shadow amount. I believe the tolerance on the revised version was/is a parallax-free plus or minus 0.3 percent.