I don't know if this matters, but I retired from an oil refinery and we did samples daily. I sent in my first two samples to BlackStone Lab and to our refinery lab. They were exact per our lab and I have been very comfortable with them since. The sample kits are free and they are quick with the sample. I like that they send an email and have access to the paperwork on line. When I had a question and call their 800#, they took the time to explain where I was totally satisfied. And the one time I had an issue with USPS trying to send in a sample, their letter helped and now no issues with the postoffice.