residual liquid junction (potential) error

in pH measurement
https://doi.org/10.1351/goldbook.R05313
Error arising from breakdown in the assumption that the @[email protected] potential remains constant when solution X is substituted for solution S in the operational cell.
Source:
PAC, 1985, 57, 531. (Definition of pH scales, standard reference values, measurement of pH and related terminology (Recommendations 1984)) on page 541 [Terms] [Paper]