Surveying Terms-what do they mean?

There is a great site about surveying called www.metesandbounds.com. They have a full collections of terms that we see on Surveys all the time, but maybe overlook their meanings. Here are a few that I found interesting. For a complete list go to the site and see what else they have to offer.

Acre - The (English) acre is a unit of area equal to 43560 square feet, or 10 square chains, or 160 square poles. A square mile is 640 acres. The Scottish acre is 1.27 English acres.
Arpent - Unit of length and area used in France, Louisiana, and Canada. As a unit of length, approximately 191.8 feet. The (square) arpent is a unit of area, approximately .85 acres.
Chain - Unit of length usually understood to be Gunter's chain, but possibly variant by locale. Chains equal to 2 poles (one half the standard length) are found in Virginia. The name comes from the heavy metal chain of 100 links that was used by surveyors to measure property bounds.
Engineer's Chain - A 100 foot chain containing 100 links of one foot apiece.
Gunter's Chain - Unit of length equal to 66 feet, or 4 poles. This unit was apparently defined as one tenth of a furlong, a common unit of length in the old days. The mile was redefined from 5000 feet to 5280 feet in order to be an even multiple of furlongs. A mile is 80 chains.
Hectare - Metric unit of area equal to 10,000 square meters, or 2.471 acres.
Vara - Unit of length (the "Spanish yard") used in the southwest. The vara is used throughout the Spanish speaking world and has values around 33 inches, depending on locale. The legal value in Texas was set to 33 1/3 inches early this century.
Benchmark - A survey mark made on a monument having a known location and elevation, serving as a reference point for surveying.
Call - Any feature, landmark, or measurement called out in a survey. For example, "two white oaks next to the creek" is a call.
Conditional line - An agreed line between neighbors that has not been surveyed.
Corner - The beginning or end point of any survey line. The term corner does not imply the property was in any way square.
Declination - The difference between magnetic north and geographic (true) north. Surveyors used a compass to determine the direction of survey lines. Compasses point to magnetic north, rather than true north. This declination error is measured in degrees, and can range from a few degrees to ten degrees or more. Surveyors may have been instructed to correct their surveys by a particular declination value. The value of declination at any point on the earth is constantly changing because the location of magnetic north is drifting.
Landmark - A survey mark made on a 'permanent' feature of the land such as a tree, pile of stones, etc.
Line Tree - Any tree that is on a property line, specifically one that is also a corner to another property.
Monument - A permanently placed survey marker such as a stone shaft sunk into the ground.
Out - An 'out' was ten chains. When counting out long lines, the chain carriers would put a stake at the end of a chain, move the chain and put a stake at the end, and so on until they ran "out" of ten stakes.
Point of Beginning - The starting point of the survey
Plat - A drawing of a parcel of land.
Witness Tree - Generally used in the public land states, this refers to the trees close to a section corner. The surveyor blazed them and noted their position relative to the corner in his notebook. Witness trees are used as evidence for the corner location.