When a pH meter’s accuracy is stated as “±0.01 pH ±1 digit,” it means two things:
1. ±0.01 pH: This is the base accuracy specification for the instrumentation alone.
2. ±1 digit: This refers to the uncertainty in the least significant digit of the display (i.e., the rounding error of the final digit).
If your meter displays values to two decimal places (e.g., 7.12 pH), then “±1 digit” corresponds to ±0.01 pH (one increment in the last digit). Therefore, in practice, the total possible error can be up to ±0.02 pH from the displayed reading (±0.01 pH base accuracy plus the ±0.01 pH from the last digit’s rounding).