Solid Calibration Standards for the TD-500D, TD-3100, and TD-4100 Series Instruments. Instantly calibrate or check instrument performance without preparing liquid standards. Insert the CheckPoint Solid Standard (patent pending) probe into the inspection port of your Turner Designs on-line oil in water monitor, or place it in the sample compartment of the lab instrument to check instrument calibration and performance. The CheckPoint Solid Standard allows operators to make instrument adjustments within minutes. CheckPoint Solid Standards are physically robust to provide accurate and repeatable results - and easy to use by both new and experienced operators. Easily tune the solid standards to a set-point matching a calibrated concentration or present limit.