I do medium voltage switchgear maintenance and repair in my job (13.2KV down to 480V). My partner thought that he heard an air leak in the gear one day, which is a sign of arcing. That range is gone in my hearing, so I used bismarkbsspectrum with my iPhone5 on the main 13.2KV breaker and took a screen shot of it, which showed a hard spike at around 10KHz. We singled up the plant and shut down that feeder the following weekend and pulled out the main breaker for maintenance... We found evidence of arcing inside the arc chutes. We cleaned, lubed, and tested the breaker and put it back into service. Afterwards, I ran bismarkbsspectrum again as before, and took a another screenshot (over-layed) on the first one.... this showed the spike was absent now. We used this comparison graph to quantify our results to upper management, which validated the expense of a weekend shutdown. Great app!