Standardization pull for a 30 m metallic tape: What pull (tension) is typically applied so that the tape reads its standardized length during measurement?

Introduction / Context:
Tapes are standardized to read true length at a specified temperature and tension (pull). Applying the correct pull minimizes systematic error from elastic stretch or slack. Metallic tapes (linen or synthetic fabric reinforced with fine wires) require relatively small standardized pulls compared with steel tapes.

Given Data / Assumptions:

• Tape length = 30 m (metallic tape, not a steel tape).
• Field temperature is assumed close to the standard (or temperature correction handled separately).
• Pull is applied steadily without jerks.

Concept / Approach:

Survey practice distinguishes metallic tapes from steel tapes. Metallic tapes are lighter, more flexible, and standardized at lower tensions, commonly around 2 kg, to limit permanent set and to reflect their elastic characteristics. Using a much higher pull (typical of steel tapes) risks overstretching and increases random error if the pull cannot be held steady. Therefore, for a 30 m metallic tape, a pull of about 2 kg is typically adopted as the standardization pull unless a specific calibration certificate specifies otherwise.

Step-by-Step Solution:

Verification / Alternative check:

Calibration data from manufacturers and many surveying manuals list ~2 kg for metallic tapes and higher values (often 5–8 kg) for steel tapes, affirming this choice.

Why Other Options Are Wrong:

1 kg may be too low to remove slack; 3–5 kg reflects steel tape standards and risks overstretching a metallic tape.

Common Pitfalls:

Applying steel-tape pulls to metallic tapes; ignoring the calibration sheet; failing to use a spring balance, leading to inconsistent tension.

Final Answer:

2 kg