Apera Instruments GroStar GS3 EC PenLab grade instruments designed specifically for growers! The GS3 EC Pen includes: 2. 77 EC calibration solution (50 ml bottle) Measures conductivity EC, PPM (500), PPM (700) and temperature Premium probe technologies and materials ensure high accuracy and durability with minimal maintenance Titanium alloy sensor designed for high accuracy EC measurement Easy to use design and fast calibration adjustment Large 3 color backlit screen gives you clear