Question:
The instrument used to measure diameter at any convenient height.
The instrument used to measure diameter at any convenient height.
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Remember: Penta Prism = Diameter at height; Relaskop = Basal area/Height/Diameter; Calliper = DBH (Direct).
Updated On: Aug 7, 2026
- Tree Calliper
- Blue Tape
- Wheeler’s Penta Prism
- Relaskop
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Question:
In forest mensuration, measuring the diameter of a standing tree at breast height (1.37m in India) is standard. However, to calculate the volume accurately or study the taper of the stem, diameters at various heights along the trunk are required. This question asks for the specific instrument designed for such remote diameter measurements.
Detailed Explanation:
• Standard Instruments: Conventional tools like Tree Callipers and Diameter Tapes are used for direct measurements at reachable heights. They cannot be used for upper-stem diameters without using ladders or climbing.
• Wheeler's Penta Prism: This is an optical instrument specifically designed to measure the diameter of a tree at any visible height from a distance. It works on the principle of reflecting two images of the tree stem through pentaprisms. One prism is fixed, and the other is movable along a graduated bar. When the two images of the edges of the tree trunk are aligned, the diameter can be read directly from the scale.
• Relaskop: The Spiegel Relaskop is a multi-purpose tool that can measure height, basal area, and diameter at height. While it is highly versatile, the Wheeler’s Penta Prism is the most direct answer for specific diameter measurements at heights because of its dedicated design for this purpose.
• Comparison: Callipers (A) and Blue Tape (B) are contact-based and limited to reachable heights. Relaskop (D) is a versatile device used for point sampling and height, but Penta Prism (C) is the specialized instrument for precise upper-stem diameter.
Step 2: Final Answer:
The instrument specifically used to measure the diameter of a standing tree at any convenient height from the ground is Wheeler’s Penta Prism.
In forest mensuration, measuring the diameter of a standing tree at breast height (1.37m in India) is standard. However, to calculate the volume accurately or study the taper of the stem, diameters at various heights along the trunk are required. This question asks for the specific instrument designed for such remote diameter measurements.
Detailed Explanation:
• Standard Instruments: Conventional tools like Tree Callipers and Diameter Tapes are used for direct measurements at reachable heights. They cannot be used for upper-stem diameters without using ladders or climbing.
• Wheeler's Penta Prism: This is an optical instrument specifically designed to measure the diameter of a tree at any visible height from a distance. It works on the principle of reflecting two images of the tree stem through pentaprisms. One prism is fixed, and the other is movable along a graduated bar. When the two images of the edges of the tree trunk are aligned, the diameter can be read directly from the scale.
• Relaskop: The Spiegel Relaskop is a multi-purpose tool that can measure height, basal area, and diameter at height. While it is highly versatile, the Wheeler’s Penta Prism is the most direct answer for specific diameter measurements at heights because of its dedicated design for this purpose.
• Comparison: Callipers (A) and Blue Tape (B) are contact-based and limited to reachable heights. Relaskop (D) is a versatile device used for point sampling and height, but Penta Prism (C) is the specialized instrument for precise upper-stem diameter.
Step 2: Final Answer:
The instrument specifically used to measure the diameter of a standing tree at any convenient height from the ground is Wheeler’s Penta Prism.
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