Surveying Chains: Gunter's, Engineer's, Revenue, Metric

• Surveying chains are tools used to measure distances in land surveying
• They are made of metal links connected by rings or swivels
• Chains are designed for accuracy and durability in field conditions

Gunter's Chain

• Gunter's Chain is 66 feet (20.1168 meters) long
• It is divided into 100 links
• Each link is 0.66 feet (7.92 inches) long
• It is primarily used for measuring distances in acres
• 10 square chains equal one acre

Engineer's Chain

• Engineer's Chain is 100 feet (30.48 meters) long
• It also consists of 100 links
• Each link is 1 foot long
• It is mainly used in engineering projects and large-scale surveys
• Measurements are conveniently read directly in feet

Revenue Chain

• Revenue Chain is 33 feet (10.0584 meters) long
• It is shorter than both Gunter's and Engineer's chains
• It is commonly used for cadastral surveys, especially in India
• The length is convenient for local land measurements and record-keeping

Metric Chain

• Metric Chains come in various lengths such as 20 meters and 30 meters
• A 20-meter chain typically has 100 links, each 0.2 meters long
• A 30-meter chain usually has 150 links, each also 0.2 meters long
• It is used in countries that follow the metric system
• It simplifies calculations by providing measurements in meters and centimeters

Chain Materials and Construction

• Surveying chains are typically made of galvanized steel to prevent rust
• The links are connected by small rings, usually three oval rings, to allow flexibility
• Handles are made of brass and are attached to each end of the chain
• Swivels are often placed at intervals to prevent twisting and tangling of the chain

Taping Corrections

• Absolute length correction is the correction applied to each tape length
• Temperature correction accounts for expansion and contraction with temperature changes
• Slope correction adjusts measurements taken on slopes to horizontal distances
• Tension or pull correction adjusts for variations in tension applied during measurement
• Sag correction accounts for the sag in the chain due to gravity

Chain Surveying Accessories

• Arrows are used to mark the end of each chain length during measurement
• Ranging rods are used to align the chain between survey stations
• Offset rods are used to measure short distances perpendicular to the chain line
• Plumb bobs are used to ensure vertical alignment when measuring slopes

Common Errors in Chaining

• Mistakes in counting chain lengths can cause significant errors
• Misalignment of the chain can lead to inaccurate distance measurements
• Variations in tension, temperature, and sag can affect the chain’s length
• Inaccurate marking of chain ends can compound errors over long distances

Advantages of Using Chains

• Chains are simple to use and require minimal training
• They are durable and can withstand harsh field conditions
• Chains do not require batteries or external power sources
• They are relatively inexpensive compared to electronic measuring devices

Disadvantages of Using Chains

• Chains are less accurate than electronic measuring devices
• They are prone to errors due to sag, temperature variations, and tension
• Chains can be cumbersome to use in difficult terrain or dense vegetation
• They require more time and labor compared to modern surveying methods