ALEX is the software used. Not the testing "method"
Did your dealer use a titrating and drop test or "accu" test system where a piece of paper with a sample of your water goes into a device?
I used the ALEX software for years with DPD tablets, droppers for pH and titrate testing for TA and CH. It was fairly accurate. That said, two people could use the lab with the same water and get different results. There is a certain variance that will occur due to the tester. I might think the colour matches, but Chas doesn't and thinks one or two more drops gets the right colour.
Cleanliness of the testing equipment can also influence results.