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Levelling or leveling (American English; see spelling differences) is a branch of surveying, the object of which is to establish or verify or measure the height of specified points relative to a datum. It is widely used in geodesy and cartography to measure vertical position with respect to a vertical datum, and in construction to measure ...
Level staff. A level staff, also called levelling rod, is a graduated wooden or aluminium rod, used with a levelling instrument to determine the difference in height between points or heights of points above a vertical datum. When used for stadiametric rangefinding, the level staff is called a stadia rod.
For double-acting single-rod cylinders, when the input and output pressures are reversed, there is a force difference between the two sides of the piston due to one side of the piston being covered by the rod attached to it. The cylinder rod reduces the surface area of the piston and reduces the force that can be applied for the retraction stroke.
A Philadelphia rod is a level staff used in surveying. The rod is used in levelling procedures to determine elevations and is read using a level. A Philadelphia rod consists of two sliding sections graduated in hundredths of a foot. On the front of the rod the graduation increasing from zero at the bottom. On the back of the rod the graduation ...
Double junction, or level junction (left hand running). A double junction is a railway junction where a double-track railway splits into two double track lines. Usually, one line is the main line and carries traffic through the junction at normal speed, while the other track is a branch line that carries traffic through the junction at reduced speed.
Common levelling instruments include the spirit level, the dumpy level, the digital level, and the laser level. Levelling staff – specialized measuring stick or vertical staff used with the dumpy level, held by a second person while the operator of the level looks through it and takes readings off of the staff. Also call a rod. Reduced level ...
Level (optical instrument) A level is an optical instrument used to establish or verify points in the same horizontal plane in a process known as levelling. It is used in conjunction with a levelling staff to establish the relative height or levels (the vertical separation) of objects or marks. It is widely used in surveying and construction to ...
The point machine (in this case an electric motor) and associated mechanism used to operate this switch can be seen to the right in the picture. A point machine (also known as a point motor, switch machine or switch motor) is a device for operating railway turnouts especially at a distance.