Ohaus Starter pH/ORP Pen MetersCompact Design for Fast, Convenient Electrochemistry Measurement At Your Fingertips OHAUS precision meters provide accurate measurement of pH and oxidation reduction potential (ORP). Starter pen meters are the economical option when you are simply looking for meters that will provide accurate measurement without restriction. Specifications Measurement Range 0. 00 14 pH; 0. 0 99. 0 C (ST20 R Only) Measurement Resolution 0. 01 pH (ST20) 0. 1 pH (ST10)