esthesiometer

noun

es·​the·​si·​om·​e·​ter

variants or chiefly British aesthesiometer

es-ˌthē-zē-ˈäm-ət-ər  -ˌthē-sē- 

: an instrument for measuring sensory discrimination

especially : one for determining the distance by which two points pressed against the skin must be separated in order that they may be felt as separate