User Guide
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05.1 · Measurement Tools

Measurement Overview and Calibration

Measurement tools compute real-world dimensions — not just on-page points — from a calibrated scale. You must calibrate once per document before measurements will produce meaningful values.

The Measurement Tools

ToolMeasures
DistanceStraight-line length between two points
PerimeterTotal length of a multi-point polyline
Area (Polygon)Enclosed area of a polygon
Rectangle MeasureWidth, height, perimeter and area of a rectangle
Circle MeasureRadius, diameter, circumference, area
CountTally markers; displays a running count (see 05.3)

All except Count produce a label showing the computed value in the current units.

Calibrating the Scale

Most architectural or engineering PDFs have a known scale (e.g. 1:100, 1:50, or "1 inch = 20 feet"). Calibration tells Spark how many real-world units correspond to one point on the page.

Workflow

  1. Tools → Measure → Calibrate Scale (or right-click the page → Measure → Calibrate Scale).
  2. A prompt asks you to draw a reference line — pick a known distance on the drawing (a dimension line is ideal).
  3. Click the start point, then the end point.
  4. A dialog asks for the real-world length of that line.
  5. Enter the value and choose Units (mm, cm, m, inches, feet, yards, etc.).
  6. Click OK.

Spark now knows the page's scale. All subsequent measurements use it.

Verifying Calibration

After calibrating, draw a Distance measurement across a dimension line with a known value and compare. If it matches (to a reasonable tolerance), calibration is good.

Recalibrating

Tools → Measure → Calibrate Scale again. The new calibration replaces the old. Existing measurements do NOT auto-update — they keep the value at time of draw. Recreate them to reflect the new scale.

Tip

Warning — If the PDF has multiple pages at different scales (a title sheet, plan views and detail sheets), calibration is per-document in the current version. For mixed-scale drawings, keep them in separate files or use a dedicated takeoff tool.

Units

Spark supports:

  • Metric: mm, cm, m, km.
  • Imperial: in, ft, yd, mi.
  • You can switch display units after calibration — the stored real-world length doesn't change, only the display conversion.

How Calibration Is Stored

The scale factor is stored in a custom PDF key and persists with the document. When you reopen in Spark, measurements recompute with the same scale.

Other PDF viewers won't see the calibration; they'll see the measurement text as a plain label.

Precision Display

Measurements display 2 decimal places by default. Configure precision in Settings → Measurement → Decimal Places.

Snap While Measuring

While drawing a measurement:

  • The cursor snaps to corners, midpoints and intersections of nearby shapes (detected on hover).
  • Hold Shift to lock the segment to 0° / 45° / 90°.
  • Press Esc to cancel the in-progress measurement.

Next

See 05.2 for the specific measurement tools (Distance / Perimeter / Area) and 05.3 for Count Markers.