Because given rotating speed of some turbofan engine can be known not through setting up mechanical devices

a data fusion arithmetic is presented to make certain of given rotating speed on the base of studying the working principle of some turbofan engine rotating speed control system and the factor of affecting given rotating speed.Through experiment

the results show that the structure of the presented data fusion arithmetic is single

its calculation is advantageous

its relative errors are in 1 %

and the presented data fusion arithmetic applying for calculating the given rotating speed of some turbofan engine is effective.