I am the manufacturer of the YM Instrument Co.,Ltd.in China. Portable pH Pen/Meter
Captive Purity Portable pH Pen/Meter YM-901

Digital pH Meter Tester - Universal Tester!
1. Pen type pH meter 2. Lightweight, compact
3. Read quickly and accurately
4. Switching film
5. Long low battery power consumption
6. Waterproof
7. Features: automatic cutoff switch
8. Low power consumption (as long as there is any view
Guarantee the accuracy)
9. Operating Temperatures: 0`C to 50`C (ATC)

This handy pH pen/meter is a great tool for any aquarist. It is extremely easy to use and is waterproof. Simply dip the meter in the solution to get the pH reading. Its high accuracy and resolution also make it suitable even for the most-demanding applications.

Note: pH 7.0 solution is required for calibration.

Specifications:

Large Readout Display
Range: 0.00-14.00 pH
Resolution: 0.01 pH resolution
Accuracy: <=+/- 0.03 pH
Fixed Electrode .changeable electrode

Operating Temperatures: 0`C to 50`C (ATC)
ATC: Automatic Temperature Compensation for accurate readings!
Power Supply: 4 x 1.5 Volt (Button Battery)
Battery Life: 1000 hours of continuous use
Size: 6" x 1.00" Largest Diameter
Weight: 70 Grams