Forklift hydraulics are controlled either with levers directly manipulating the hydraulic valves or by electrically controlled actuators, using smaller "finger" levers for control. The latter allows forklift designers more freedom in ergonomic design. Forklift trucks are available in many variations and load capacities. In a typical warehouse setting, most forklifts have load capacities between one and five tons. Larger machines, up to 50 tons lift capacity, are used for lifting heavier loads, including loaded shipping containers. In addition to a control to raise and lower the forks (also known as blades or tines), the operator can tilt the mast to compensate for a load's tendency to angle the blades toward the ground and risk slipping off the forks. Tilt also provides a limited ability to operate on non-level ground. Skilled forklift operators annually compete in obstacle and timed challenges at regional forklift rodeos. Powered pallet truck, usually electrically powered. Low lift trucks may be operated by a person seated on the machine, or by a person walking alongside, depending on the design. May be internal combustion engine or electrically powered. Usually electrically powered. A stacker may be operated by a person seated on the machine, or by a person walking alongside, depending on the design. Variant on a Rider Stacker forklift, designed for small aisles, usually Electrically Powered, named because the forks can extend to reach the load. There are two variants, moving carriage, which is common in North America, and moving mast which is common in the rest of the world, and generally regarded as safer   Comes in Stand on End Control, Stand on Center Control, and Sit Down Center Control, which is the most numerous   Comes in Stand on End Control, and Sit Down End Control, which is the most numerous. It may be electrically powered, or have an internal combustion engine. Engines may be diesel, kerosene, gasoline, natural gas, butane, or propane fueled, and may be either two-stroke spark ignition, four stroke spark ignition (common), two-stroke compression ignition, and four-stroke compression ignition (common). North American Engines come with advanced emission control systems. Forklifts built in countries such as Iran or Russia will typically have no emission control systems. Some sideloaders have hybrid drivetrains. Comes in Stand on Center Control, and Sit Down Center Control, which is the most numerous. Usually has an Internal Combustion Engine.