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Producing ready mixed concrete relies on accurate proportioning and weighing of materials before they are even put in the mixer. Water and admixtures are measured by volume, but cement, sand and aggregate must be measured by weight. Weigh batchers guarantee consistency and ensure that concrete is batched correctly by measuring specified amounts of sand, cement, and aggregate. There are two types of weigh batchers--mechanical and electronic. Mechanical batchers use springs to measure weight and are now used primarily as backup systems for electronic batchers. Electronic scales are more frequently used today. They are suspended by load cells which convert force into a measurable electric quantity. Computer systems are available that work in conjunction with electronic batchers to bring a high level of efficiency to the batching process. Electronic batchers can be categorized into two divisions: stationary and nonstationary batchers. Stationary batchers consist of a fixed hopper that is hung from one or more load cells. This choice of batcher is common for stack plants where the batcher is mounted above the mixer. There are several types of nonstationary batchers, including stationary belt conveyors, skip hoists, and traveling batchers.