Abstract: Based on the dynamic equation for the tachometric wheel of welded-pipe flying saw,a study concerning the wheel's following-up characteristics is made,involving such aspects as following-up time,measurement tolerance and contact pressure vs measurement tolerance relationship,etc. For the first time,formulas for calculating the tachometric wheel measurement-tolerance and the wheel's contact pressure against the pipe are derived,providing a theoretic basis for design of the tachometric wheel and tachometric mechanisms as well.