Staff readings: lower cross hair = 1.4 m, upper cross hair = 2.9 m. Instrument has anallatic lens. Calculate horizontal distance between staff and instrument.
Correct Answer: C. 150 m
📚 Detailed Explanation: Anallatic Lens Tacheometer — Horizontal Distance = 150 m
Why C (150 m) is correct: The staff intercept S = upper hair − lower hair = 2.9 − 1.4 = 1.5 m. With an anallatic lens (K = 100, C = 0): D = 100 × 1.5 = 150 m.
Given:
Lower stadia hair reading = 1.4 m
Upper stadia hair reading = 2.9 m
Lens type: ANALLATIC (K = 100, C = 0)
Lower stadia hair reading = 1.4 m
Upper stadia hair reading = 2.9 m
Lens type: ANALLATIC (K = 100, C = 0)
Step 1: Staff intercept
S = Upper – Lower = 2.9 – 1.4 = 1.5 m
Step 2: Distance formula
D = KS + C = 100 × 1.5 + 0 = 150 m
Stadia Reading Interpretation
| Cross Hair | Reading (m) | Function |
|---|---|---|
| Upper stadia hair | 2.9 | Upper boundary of intercept |
| Middle (central) hair | ~2.15 (midpoint) | Used for reading height above ground if needed |
| Lower stadia hair | 1.4 | Lower boundary of intercept |
| Staff intercept S | 2.9 − 1.4 = 1.5 m | Used in distance formula |
- S = 2.9 − 1.4 = 1.5 m.
- D = 100 × S = 100 × 1.5 = 150 m.
- Anallatic lens: K = 100, C = 0 → D = 100S always.