The pH 4 reference solution (for use with the SC-200 or SC-300 unit + pH electrode) is now labeled as 4.00, the correct reference value at a temperature of 20 ℃ (68 ℉). The chemical composition of the solution itself is unchanged from before, and its reference value is still 4.01 at 25 ℃ (77 ℉). It’s just that since most of us work on wine or other beverages that are closer to 15 to 20 ℃ (59 to 68 ℉), a value of 4.00 is slightly more accurate than 4.01. Instruments that use the old reference value 4.01 rather than the new value of 4.00 do not produce significant error: less than 0.02 pH difference in wines with pH values from 3.00 to 4.00.
As mentioned in a recent newsletter, we have a new update to the firmware for SC-200s and -300s built after 2015 (Serial numbers 2897 and above for SC-300s, 470 and above for SC-200s). This new firmware, versions 3.2.F (or 2.2.F for an SC-200) and higher, uses the value of 4.00 instead of 4.01 for pH calibration. All new units being shipped will now have this new firmware version installed on them. If your instrument has a lower serial number, or an earlier version of firmware, it will set the pH 4 reference to 4.01 as usual.