refractometer testing of coolant, is ATC important?

Randy,

In my experience it won't matter. I normally check our coolant at room temperature and the OEM recommends a ratio of 3-5 percent for our coolant type. Being off by a percentage or so in most cases isn't going to be significant for any concerns. Of course there are some that have radical machining conditions where the daily volume of coolant and temperature rapidly changes and therefore could be more of a concern. Anyway, always follow what is documented from the OEM is my best recommendation for you in normal conditions.

H> How far off will the readings be if my refractometer is not an