I couldn't get the web or app tuner to work consistently, so I downloaded the firmware 6.4.0 release candidate, updated the printer, and used the belt tuning wizard. The wizard was very easy to use; it even recommends how far to turn the tensioners. If you do this, feel free to set up Wi-Fi, but skip calibration for now. You'll do it in a few steps once the belts are tuned and the print bed is installed.
I started following the belt tensioning guide, and the first suggestion was to use the built-in tuner in the printer itself. But I was unsure about that since I have not yet booted it up? I then tried the website app, but that didn't pick up my microphone. Then, I installed the prusa app on my android, and that worked as expected.
Tried the web site and it would only show frequency occasionally and could not use it. I do not have an android device so the app would not work. Tried some iphone frequency analyzer apps and just to sensitive to other noises in house. Tried my guitar tuner and just not enough volume from belt. Broke down and got a stroboscope on Amazon for $99. Worked perfectly. you just need a dark-ish room
I think that the latest firmware of the COre One has a stroboscobe effect by itself. It uses the LED strip ounted in the front bar of the Core XY sheet. You' ll see this when you power up the machine.
I could not get the tuner app (phone or web) to work. I also tried multiple other suggested apps for tunning by frequency, none of them worked. This simple print worked for me the on the first try: https://www.printables.com/model/1312851-prusa-core-one-belt-tension-gauge
For me I found a needles width away from max worked. I just had to make sure both belts were the same. Hope this helps someone else.
For me I found a needles width away from max worked. I just had to make sure both belts were the same. Hope this helps someone else.