Among the following factors that can cause an error during distance measurement in chaining, the compensating error is caused by:
📝 Detailed Explanation: Compensating vs. Cumulative Errors
In surveying, it's crucial to understand the different types of errors that can occur. The question asks to identify a compensating error.
What are Compensating Errors?
Compensating errors (also called accidental or random errors) are unpredictable and have an equal chance of being positive or negative. They arise from imperfections in human senses and limitations of equipment. For instance, when marking the end of a chain, an assistant might mark a point slightly ahead of the true end on one measurement, and slightly behind on the next. Over a long survey line with many measurements, these small, random errors tend to cancel each other out, so they don't significantly affect the final result.
Careless holding and marking is a classic example of this. It's a random human error that can go in either direction.
What are Cumulative Errors?
In contrast, the other options are cumulative errors (or systematic errors). These errors always have the same sign (either always positive or always negative) and thus accumulate over time, leading to a large total error.
- (a) Variation in temperature: If the temperature is higher than standard, the chain will be consistently too long for every measurement, causing a cumulative negative error.
- (b) Sag in chain: The sag always makes the measured distance longer than the true horizontal distance, resulting in a cumulative positive error.
- (d) Bad ranging: If the chain is not aligned in a straight line, the measured distance will always be greater than the true straight-line distance, leading to a cumulative positive error.
Classification of Errors in Chaining
The table below provides a clear classification of common errors encountered during chain and tape surveying.
| Source of Error / Case | Type of Error | Sign (+/-) |
|---|---|---|
| Incorrect length of tape/chain | Cumulative / Systematic | + or – |
| Tape not stretched horizontally | Cumulative / Systematic | + |
| Error due to sag | Cumulative / Systematic | + |
| Tape not stretched tight & straight (Bad Ranging) | Cumulative / Systematic | + |
| Error due to temperature | Cumulative / Systematic | + or – |
| Variation in pull | Compensating / Random | + or – |
| Careless holding & marking | Compensating / Random | + or – |
| Disturbing arrows after they are set | Blunder / Mistake | Gross Error |
| Incorrect counting of tape length | Blunder / Mistake | Gross Error |