The distance between steps for measuring downhill to obtain better accuracy

⛰️ Understanding the "Stepping" Method

When measuring distances on sloping ground, the goal is always to find the true horizontal distance, not the longer slope distance. The "stepping" method (or "breaking chain") is a technique used to achieve this. The total length is broken down into shorter, more manageable segments, and the horizontal distance of each segment is measured one by one.

This is especially important when measuring downhill, as the forward chainman must hold a section of the chain horizontal and use a plumb bob to mark the end point on the ground.

🔬 The Challenge of Steep Slopes

The accuracy of the stepping method is directly affected by the steepness of the slope. As the ground becomes steeper, several problems arise if the step distance is too long:

• Difficulty Keeping the Chain Horizontal: The steeper the slope, the greater the vertical drop. It becomes physically very difficult for the forward chainman to hold their end of a long tape high enough to keep it perfectly level.
• Plumb Bob Error: A longer vertical drop for the plumb bob increases the chance of error. The bob is more likely to be affected by wind or slight movements, leading to inaccurate marking of the point on the ground.
• Chain Sag: A longer, unsupported section of the chain will sag more under its own weight, leading to an overestimation of the horizontal distance.

💡 The Solution: Shorter Steps

To counteract these challenges and maintain high accuracy, the field procedure must be adapted to the steepness of the terrain.

The solution is to decrease the distance of each step as the slope increases. By taking shorter horizontal steps:

• The vertical drop becomes smaller and more manageable.
• It's easier for the chainman to hold the shorter section of the tape truly horizontal.
• The plumb bob is used with a shorter string, making its marking far more precise and less susceptible to wind.
• Sag in the shorter tape segment is significantly reduced.

Therefore, to get better accuracy, the distance between steps must decrease as the slope of the ground increases.