how to understand your Standardise method - dataframe div first row

[elulue]

Dears,

I am confused about the standardise method in the code -

    def zero_base_standardise(self, data, abs_base=pd.DataFrame()):
        """Standardise dataframe to be zero based percentage returns from i=0"""
        if(abs_base.empty): abs_base = data.iloc[0]
        data_standardised = (data/abs_base)-1
        return (abs_base, data_standardised)

My understanding about the standarise is -

(x - mean) / standard_deviation
mean = sum(x) / count(x)
standard_deviation = sqrt( sum( (x - mean)^2 ) / count(x))

I think (data/abs_base)-1 should be far from standardised values, could you please kindly let me know if I misunderstood anything?
Thank you very much!