How did Ivan Pavlov measure the strength of conditioning in dogs?

Ivan Pavlov measured the strength of conditioning in dogs by observing and recording the occurrence of a conditional response—specifically, the amount of salivary secretion elicited by a conditional stimulus, such as the ticking of a metronome.12

In his systematic experiments, Pavlov restrained a hungry dog and presented a neutral stimulus immediately before providing food, which served as an unconditional stimulus that naturally triggered salivation. By repeatedly pairing these stimuli, he established a conditioned reflex. He measured the strength of this learning by observing how reliably the conditional stimulus alone could trigger the salivation response. Furthermore, he studied the persistence of this behavior by observing the process of extinction, where the conditional response gradually disappeared if the conditional stimulus was repeatedly presented without the reinforcement of food.2