Ventisonic Digital LCD Monitor PH Meter Tester Pen with Backlight Test Water Pool Hydroponic Aquarium Monitor Red Compact and portable pen-type design Built with Automatic Temperature Compensation (ATC); BATTERY: 4 x 1.5v (AG-13) High accuracy 0.1 pH; pH measuring range : 0.00 - 14.00 pH; Backlight LCD Automatic Temperature Compensation : 0 - 50 C (32 - 122 F); Operating Temperature : 0 - 50 C (32 - 122 F); Package Included: 1 x Digital pH meter; 1 x Calibration Adjustment screwdriver; 1 x User instruction; 2 x calibration buffer solution