This instrument, though labeled as glossodynamometer, is an dynamolabiometer, that was designed and produced by French instrument maker Charles Verdin. It was used to measure the strength of the lips to resist pressure. The lips are pressed against the small disc fixed on a steel rod of this special kind of a dynamometer, the maximum possible compression of the spring in the instrument handle can be read at its end.
Variations of this instrument with springs of different strengths were also used to measure the force of the tongue (glossodynamometer) and even the blood pressure (sphygmometer). In the context of this source it is used to control the success of exercises for tongue and lips of the deaf.