Apparatus to measure the physical characteristic of an object. There is a main body to receive the object. There is a device to enable the operator to determine when the object is correctly on the body. A piezoelectric ultrasonic transmitter sends a signal through the object. The transmitter comprise a first hollow container slidably received in the main body and a piezoelectric ceramic transmitter resiliently mounted in the first container. Transmitter is urged towards the object but its movement is restricted. A piezoelectric ultrasonic receiver spaced from the transmitter also projects towards the body. The receiver comprise a second hollow container slidably received in the main body. A ceramic transducer is resiliently mounted in the second hollow container. A signal is generated to be transmitted. The signal can be amplified. In a preferred embodiment the object is a foot and the device is useful in determining the presence of a osteoporosis. A method of measuring the physical characteristic of an object is described. The object is subjected to resonating frequencies in the same piezoelectric ultrasonic transmitter. A first resonating frequency obtained by resonating the thickness mode is obtained and the second lower resonating frequency obtained by resonating the radial mode is obtained. From these measurements the physical characteristics of the object can be deduced.