vibrating-reed tachometer

vibrating-reed tachometer

[′vī‚brād·iŋ ¦rēd tə′käm·əd·ər]
(engineering)
A tachometer consisting of a group of reeds of different lengths, each having a specific natural frequency of vibration; observation of the vibrating reed when in contact with a moving mechanical device indicates the frequency of vibration for the device.