Quick answer:
A PDR line board makes panel shape visible by reflecting a regular stripe pattern across the repair area. When reflected stripes cross a low, they generally spread or widen; when they cross a high, they generally pinch or crowd together. Use that relationship as a directional cue, then compare it with nearby undamaged metal from more than one viewing angle. Board orientation, viewing angle, strong curvature, and the transition between a crown and its center can change the apparent distortion, so one reflection is not a final diagnosis.
What a line board measures
A line board does not identify a repair move by itself. It gives the technician a repeatable visual reference: straight stripes on a clean section, and a departure from those stripes where the panel shape changes. The useful observation is the difference between the damaged area and a nearby reference area with the same general contour. The inference comes later: whether that difference is a low, an isolated high, a crown, a residual wave, or simply glare.
Set the board and your eye position before touching the panel. A board placed for a shallow door ding may be unsuitable for a long crease or a tight body line. Keep enough clean panel in the reflection to compare the line spacing and direction on both sides of the damage. This is the same reason a technician checks a repair with several views rather than declaring the panel finished when one stripe happens to look straight.
The professional training explanations from Learn PDR Online and Dent Time show how a line board makes reflected panel distortion readable and support the core directional cue: lows generally widen the reflected lines, while highs generally pinch them. The expanded confirmation method below is SuperPDR's editorial diagnostic sequence, not a workflow attributed to either source.
Reflection decision table
| Observable reflection cue | Working interpretation | Confirmation check | Next action |
|---|---|---|---|
| Stripes spread or widen across a depression | Low area | Compare the spacing with clean metal at the same angle | Locate the center before a light push or pull |
| Stripes pinch or crowd at one point | Isolated high | Move the board slightly; a true high should remain localized relative to the reference | Reduce the high with controlled knockdown work, then re-read |
| Broad outward change around a low | Crown or surrounding tension | Follow the pattern beyond the visible center and compare both shoulders | Blend the crown before forcing the center upward |
| A tiny tight change that appears only when the tool is near it | Tool-tip high or pressure mark | Remove tool pressure and watch whether the localized pinch remains | Back off, reduce the high early, and reset the tip position |
| Alternating small width changes after the main dent is raised | Residual wave or uneven texture | Sweep the reflection across the area instead of staring at one stripe | Use smaller finishing corrections and recheck from another angle |
| Lines wash out, double, or disappear | Glare or poor contrast | Change board height or brightness without changing the panel | Reposition for a readable reference before diagnosing metal |
| The pattern reverses or cannot be matched to clean metal | Ambiguous orientation | Turn the board or change your viewing angle and compare the same contour | Do not act on the first impression; reorient and confirm |
This table separates what you can see from what you conclude. Widening is an observable pattern; calling it a low is a working inference that needs a clean reference. The distinction matters most around strong curves, body lines, and crowns, where the same stripe can change direction as the board or viewer moves.
Set the board before reading the dent
Place the board so its stripes cross the damage and continue onto an undamaged part of the same panel. Start far enough away that the stripe spacing is readable rather than blown out by glare. Then adjust height, angle, and brightness one at a time. Changing several variables together makes it difficult to tell whether the panel or the setup changed the pattern.
For a round door ding, let the stripes cross both the center and the outer tension area. For a crease, rotate the board until you can read the length of the distortion as well as the center. For repeated hail work, a stable mounting position can make comparisons more consistent from dent to dent; the broader workflow in the hail damage PDR guide helps put that inspection step in sequence.
Do not assume that a brighter board is always easier to read. Excess brightness can erase stripe edges on glossy paint, while too little contrast can hide a small residual wave. The aim is a clear reference pattern, not maximum output. A model-neutral board or inspection light is enough for this explanation because unresolved product identifiers should not be treated as settled technical facts.
Low spots, highs, and crowns
The basic rule is straightforward: a low generally spreads or widens the reflected stripes, and a high generally pinches or crowds them. Read "generally" carefully. Reverse board orientation, a different viewing angle, strong panel curvature, and the crown-to-center transition can alter how the pattern appears. That is why a technician should first identify a stable clean reference area and then make a small viewing change to test the interpretation.
An isolated high usually has a concentrated effect: the crowding stays near one point as you make a modest board or head movement. A low often occupies a broader zone, especially after a glue pull or on a stretched impact. Neither appearance tells you how much force to use. It tells you where to inspect next and whether a light push, pull, or knockdown is more plausible.
A crown is not simply the opposite of the center. It is surrounding tension that can affect the way stripes transition from clean panel to low. If the outer pattern is carrying tension, pushing the center aggressively can create a new high or lock in a wavy finish. Follow the reflection away from the center, compare both sides, and use controlled crown blending before asking the low to move much.
Three-angle confirmation workflow
SuperPDR uses this numbered editorial diagnostic sequence before committing to a stronger repair move. It is deliberately short so it can be repeated after each meaningful change.
- Primary view: Align the board so stripes cross the suspected defect and extend into clean metal. Note whether the stripes widen, pinch, bend, or lose contrast relative to that reference.
- Offset view: Move your head or board slightly sideways while keeping the same reference area visible. Confirm whether the suspected low, high, or crown remains in the same panel location rather than moving with glare.
- Cross view: Rotate or reposition the board to read across the other axis of the damage. Confirm that the remaining distortion has a consistent direction before selecting the next push, pull, blend, or knockdown action.
This workflow is especially useful when learning tool-tip placement. Apply only enough pressure to make the tip visible in the reflection, then release it. If the reflection changes at the expected low and returns cleanly when pressure stops, the tip is more likely to be positioned usefully. If a localized pinch remains after the pressure point, treat it as a possible new high and reduce it before continuing.
Using the reflection during repair
With a rod or hook, use the board to place the tip under the working low, not beside the visible mark. A small off-center push can produce a high that is easy to miss in normal light. With glue pulling, center the tab according to the confirmed low and inspect immediately after each pull; an overpull is a surface condition to reduce, not a reason to pull again.
The reflection also helps choose a smaller correction as the panel improves. Early repair work may address the main low and surrounding crown. Finishing work looks for residual waves, tiny tip highs, and transitions that only appear as the board moves. That sequence complements the decision framework in the PDR tool selection guide: choose the tool role after the visual diagnosis, not before it.
Stop conditions and limits
Stop and reorient the board when you cannot compare the suspected defect with a clean reference area of similar contour. A reflection that is washed out by glare, broken by an edge, or distorted only at one extreme angle is not a reliable basis for force. Change board position, viewing angle, or contrast until the clean area and repair area can be read together.
Also stop the current correction when a light push or pull creates a localized pinch, a new wave, or a change that cannot be confirmed from the offset and cross views. Reduce the developing high, reassess the crown, and use a smaller correction. If paint damage, access limitations, or an uncertain panel condition prevents a controlled inspection, do not infer repairability from the line board alone; inspect the surface and follow the appropriate repair process.
Finishing and final inspection
The final stage is a comparison exercise. Sweep the board slowly across the repair, use both the primary and cross views, and look for texture differences between repaired and original paint. A panel should not only look acceptable at one board position. It should maintain a stable reflection as you move through the reasonable working angles for that panel.
For final inspection, check the main low, the surrounding crown, possible tool-tip highs, and residual waves separately. A fog or gradient board can help make subtle texture easier to see, while a striped board is often clearer for locating direction. Neither style replaces the other in every situation. Choose the one that makes the remaining surface difference readable, then verify the result with another view.
Short FAQ
Do widened stripes always prove a low?
No. Widened stripes generally indicate a low when they are compared with a clean reference, but board orientation and curvature can change the apparent pattern. Confirm it from a second angle before moving metal.
Can a line board show paint damage?
It can reveal a texture change, but it cannot replace direct paint inspection. Stop relying on the reflection alone when you suspect a crack, chip, or coating issue, and inspect the surface closely.
For concise setup and buying answers, see the PDR line board FAQ.
Editorial review
- Super PDR: SuperPDR Editorial Team
- Review date: 2026-07-14
- Review basis: Editorially checked against the listed professional PDR training sources; no individual technical reviewer is claimed.
- Revision note: Corrected the low/high reflection guidance: lows generally spread or widen reflected stripes, while highs generally pinch or crowd them.