From Sam Chui's video, there are tiny circles on the surface of three fan blades of next generation Trent 1000 engine. Why aren't they present on remaining fan blades? Below comments suggest they are for optical purposes. What optical information can be inferred from these circle?

My prediction: They are embedded explosive charger to test explosion testing(specifically Blade off testing of an engine.

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  • $\begingroup$ At about 14:11 in the linked video the engineer talks about installing an explosive bolt to test engine containment. He's not referring to the small circles, so whatever they are for, it's not that! $\endgroup$ – CatchAsCatchCan May 20 at 12:01
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    $\begingroup$ Explosive charges would be at the root of the blade, not distributed of the entire Surface. They could be static pressure measurement points or strain gauges. But I suspect they are markers for an optical measurement system. $\endgroup$ – DeltaLima May 20 at 12:01
  • $\begingroup$ my guess is that they're nails to keep the blades in place with the frame, but I'm not sure. $\endgroup$ – Air Canada 001 May 20 at 14:23
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    $\begingroup$ @DeltaLima since they are on both the composite painted surfaces and the stainless leading edges I'm going with stickers for some optical purpose also. $\endgroup$ – John K May 20 at 14:35
  • $\begingroup$ I'm guessing that they are all on a slightly different radius. That would make it easier for a laser to focus on one at a time and so measure defomation/vibration under load at that point. $\endgroup$ – Martin James May 24 at 6:25

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