yeah it is hard we had a $250,000 rod on the dyno with a 80k engine.... concentration, space and quiet when you need it are paramount to getting a good result. I prefer to keep bystanders on these type of jobs to a minimum (owner, tuner, engine dyno or engine builder only)
For general customers who are happy to have freinds watch thier car on the dyno... no dramas but now and again we do have closed tuning sessions also.