This invention provides a particle size distribution measuring apparatus, which has a function of informing an operator of a procedure of validation work of the particle size distribution measuring apparatus. The present invention discloses an efficient method for providing answers to queries under parametric aggregation constraints. Each collar has a nonactivated state and an activated state, wherein in the nonactivated state the balloon is rotatable about the collars and each lip portion is constructed and arranged to abut a portion of the balloon to prevent the balloon from moving longitudinally relative thereto. The raised insulating cover extends over at least a portion of the sensor electrode whereby the sensor electrode is positionable adjacent to the subterranean formation for electrically coupling thereto without direct contact therewith. Dry nitrogen is sealed in the sealing structure.