Overview

When recording and reviewing control points in the Dusty Robotics FieldPrinter iPad app, operators will see both Error values and Difference (Delta) values. These two metrics serve different purposes and are calculated differently.

Understanding the distinction helps operators correctly interpret control quality, identify problematic points, and make informed decisions before printing.

What You’ll See

• Error values listed per control point
  • Each recorded control point shows an individual Error value directly in the control point list view.
  • This value appears alongside the control point name or ID.
  • Operators review this list immediately after recording control points during stationing.
  • This view makes it easy to spot individual points with higher Error values.
• Difference (Delta) values visible in Station Information
  • Difference values are not shown in the main control point list.
  • To view Difference values, tap the Station Information button located below the control point list.
  • This opens a detailed, point-to-point Delta list.
• Difference list length increases with more control points
  • The Difference list grows significantly as more control points are recorded.
  • Each control point is compared against others, resulting in many Difference entries.
  • Although the list becomes longer, recording more control points is always best practice and improves overall alignment and confidence in the station.

Why This Happens

Error and Delta are not measuring the same thing:

• Error reflects how much correction the FieldPrinter system applies to align an individual control point into the overall control network.
• Difference reflects the horizontal disagreement between control points when compared against each other.

Because they use different dimensions and calculations, the values will not always match.

How to Fix or Prevent

Control Point Error

• What it measures
  • The total adjustment applied to a single control point during stationing.
  • Calculated using X, Y, and Z values.
• What it means
  • Error represents how far the system had to move that point to achieve the best-fit alignment.
  • This includes horizontal position and elevation differences.
• How to interpret it
  • A higher Error value indicates that the control point does not align well with the rest of the control network.
  • Elevation differences alone can increase Error, even if horizontal placement is good.

Control Point Delta

• What it measures
  • The difference in measurement between control points.
  • Calculated using X and Y only.
• What it does not include
  • Difference does not consider elevation (Z).
• What it means
  • Difference highlights horizontal disagreement between control points.
  • It is useful for identifying control points that are out of position in plan view.
• How to interpret it
  • A high Difference value indicates that one or more control points are horizontally inconsistent.
  • Elevation issues will not affect Difference.

Example: Flat Floor Assumed in the Model vs Real-World Slab Variation

It is very common for project teams to assume that all control points on a floor are at a single elevation.

• In the digital model
  • Control points are often authored with the same Z-value.
  • This value is commonly set to zero (0) or a single reference elevation.
  • The model assumes the floor is perfectly flat.
• On the jobsite
  • Concrete slabs are never perfectly flat.
  • Small elevation changes are normal.
  • In some cases, slabs can have significant high and low spots.

What This Looks Like in Practice

Consider a station where:

• All control points were modeled at Z = 0.
• The slab is generally flat in plan (X and Y), but varies slightly in elevation.
• Each control point is horizontally correct relative to the others.

When these control points are recorded:

• Difference values remain low
  • Difference only considers X and Y.
  • Since the points are horizontally consistent, Delta stays within tolerance.
• Error values increase
  • Error includes X, Y, and Z.
  • The system must apply vertical corrections to account for slab variation.
  • These Z adjustments increase the Error value for individual points.

In this scenario, a high Error value does not indicate poor horizontal control. It reflects real-world elevation differences between the slab and the simplified digital model.

Best Practices

• Expect higher Error values when all control points share a single modeled elevation.
• Use Difference to evaluate horizontal consistency between control points.
• Use Error to understand total correction, including slab elevation variation.
• Do not remove a control point solely due to high Error if Difference is low and the point is known to be horizontally accurate.
• Capture more control points to reduce the influence of local slab highs and lows and improve overall best-fit alignment.