Titratable acidity measuring norms are country dependent.  If you reside in Australia, New Zealand, South Africa, the United States or Canada, the convention is to measure titratable acidity at pH 8.20.  If in Europe, the convention is to measure titratable acidity at pH 7.00.  Most titratable acids found in wine will be captured (as protons) when titrated with a strong base to pH 7.00.  Some additional protons however can often be captured if we extend the endpoint to pH 8.20.  Titratable acidity values taken at pH 8.20 versus pH 7.00 are typically 5-10% higher.