The revenue chain is:

🔑 Key Points
→ Chain surveying is the simplest method of surveying, with measurements taken in the field and supplementary work like plotting and calculations done in the office.

🔧 Sub-heading 2
→ Revenue chain: 33 ft long, used by the Revenue Department of India, with 16 links, each 2.5 ft.
→ Gunter's chain: 66 ft long with 100 links, each 0.66 ft or 7.92 inches. This length is selected for convenience in land measurements.
→ Engineer's chain: 100 ft long, consisting of 100 links, each 1 ft long. Brass rings are provided at every 10 links for indication.

📌 Important Points
→ Chains used in surveying are essential tools for accurate land measurements and come in various lengths for specific applications.

📝 Additional Information
→ Metric chains, commonly used in India, are available in lengths such as 5, 10, 20, and 30 meters, with tallies provided at every 2m for quick reading.

Explanation:
Chain surveying is the simplest method of surveying. Measurements for this survey are taken on the field and other supplementary works like plotting and calculations are carried out in the office. The measurements in chain surveying are linear. Chain, tape, ranging rod, arrows, cross-staff, offset rods, and plumb bob are the tools required for chain surveying.
Types of chain:

Revenue chain: The revenue chain is 33 ft long. It is used by the Revenue Department of India. The number of links is 16, each link being 2.5 ft.
Gunter's chain: It is also known as the surveyor’s chain. It comes in standard 66 ft. This chain consists of 100 links, each link being 0.66 ft or 7.92 inches. The length 66 ft is selected because it is convenient in land measurements.
Engineer’s chain: This chain comes in 100 ft length. It consists of 100 links, each link being 1 ft long. At every 10 links, a brass ring or tags are provided for indication of 10 links. Readings are taken in feet and decimal.
Metric chain: Metric chains are the most commonly used chain in India. These types of chains come in many lengths such as 5, 10, 20, and 30 meters. The most commonly used is a 20m chain. Tallies are provided at every 2m of the chain for quick reading. Every link of this type of chain is 0.2m. The total length of the chain is marked on the brass handle at the ends. Metric chain – 30 m (150 links) or 20 m (100 links).