He just only told me that because he use shimano sit bone tools ,the measurement chart is only for shimano saddles,it maybe not suitable to other brand saddles.
He gave me to see the chart below ,the 13cm sit bone width should be choosen 142 or 152 based on shimano pro saddle,see pic below.I found the chart on internet same as the fitter told me
https://www.rideshimano.com/global/e...erfect-saddle/
also he told me it depend on the shape of the saddle..........