A pH meter, also called a pH tester, measures the acidity and alkalinity of a liquid or other substance, on a scale with a range of 0 to 14, where 7 is neutral, 8 to 14 alkaline, and 0 to 6 acidic. pH meters have varying range, resolution, and accuracy. A pH meter has a range of applications, including soil-testing, water-testing such items as hot tubs, swimming pools, and fish tanks, and testing of other substances such as beer, wine, food or leather. A pH meter can have a combined functional application, such as a pH meter combined with oxidation reduction potential (ORP), dissolved oxygen (DO), electrical-conductivity (EC), total dissolved solids (TDS), millivolt (mV), resistivity, salinity, or temperature tester measurement. A DO/pH meter can be used as a soil pH tester. A pH meter can have one-point, two-point, or more calibration for accuracy, and can either have manual or automatic temperature compensation (ATC). ATC provides accurate readings in fluctuating temperatures. A pH meter, such as many Hanna pH meter products, feature a digital, LCD screen. A digital pH meter can also have backlighting (or backlit display) for readability. A digital pH meter can have a single-line or multiple-line display for ease of viewing and for display of indicators. A pH tester can be a handheld or benchtop model. A handheld pH tester is portable and suitable for field or lab applications. It comes either in a shape that can fit in the palm of the hand (with electrode attachment capability), or in a smaller, wide and flat shape that can be grasped with fingers for electrode immersion applications. A benchtop pH meter is usually stationary and commonly used in lab settings. A pH meter may have waterproof or dustproof housing and may have an Ingress Protection (IP) rating. Some pH meters have a hold function which freezes readings for recording, or an auto shut-off to extend the life of the batteries. A pH tester can be electrical, or battery-powered. A pH tester may have a replaceable electrode, or can come with one or more separate electrodes. pH meters are commonly used by researchers, manufacturers, educators, and hobbyists in hydroponics, aquaculture, and agriculture.