Do you need "a" number, or do you need "the" number?
Sometimes, the quick-and-dirty test you can do yourself is good enough to answer the question that's being asked.
Setting up and running the test yourself often gives insight into the function of a device that you can't gain by hiring someone else to do it.
Also offers the flexibility to chase down the cause(s) of unexpected results without doubling the cost of the test.
Not meant to replace the authority of a reputable test laboratory with the right apparatus following a well-planned procedure, of course.
STF