Shine a light into the gap to the left of each thumbwheel. A flashlight, penlight or Tensor light may be used. It is helpful, or may even be necessary, to pull each thumbwheel as far as it will go to the right, to make the gap on the thumbwheel's left as wide as possible. Try the thumbwheel in each of its ten positions. In one of the ten positions, you will get the brightest reflection, from a flat surface on a cam next to the thumbwheel. The flat surface is like a mirror. You can rotate the thumbwheel forward and backward slightly to see if the reflection comes and goes. This helps verify that you have found the flat surface.

Now, turn each thumbwheel half a turn (five positions either way.) This will be the combination and the lock will open. For example, the thumbwheels showed 8725 at the brightest reflections. The dials were each turned 5 positions to 3270 and the lock opened.

The picture above shows what to look for. Just to the left of the digit 2 in 3325, you see the reflection, from the bottom of the yellow bar to the bottom of the brown bar. (The lock doesn't really have yellow and brown bars, that's just how the picture came out.) The camera angle wasn't right to capture reflections to the left of the 3s. Some of the reflection to the left of 5 is visible. Note that this visual method works well on a new lock but may not work well after the lock has corroded and gathered dirt.

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The Feeler Gauge Method

Lockbox Use Precautions
Recovering the Combination for the Master Key Storage Lock
Using the Visual Method