Fluid flow measuring instrument

A fluid flow measuring instrument which measures a flow rate of fluid using a propagation time of an ultrasonic wave through the fluid, comprising:

• a first clock configured to output a first clock signal;
• a second clock configured to output a second clock signal faster than the first clock signal;
• a measurement control section configured to perform measuring operations at regular intervals in which the propagation time is measured, using the second clock signal;
• and
• a clock control section configured to count the regular intervals, using the first clock signal, to have initiated the measuring operations by the measurement control section and activate the second clock only for a time period needed for the measuring operation by the measurement control section.