1. A method of standardizing data used for monitoring an aeroengine, the method comprising: collecting time-series measurements over time concerning said aeroengine; from said time-series measurements, calculating a set of indicators Y=(y 1 ,. .. , y j ,. .. , y m ) that are specific to elements of said engine; from said time-series measurements, identifying an exogenous data set X=(x 1 ,. .. , x n ), representative of external context acting on said set of indicators Y; for each indicator y j of said set of indicators Y, constructing a projection space E (j) =σ(Y (j) , X) generated by analytic transformations of a subset of indicators Y (j) =(y 1 ,. .. y j−1 , y j+1 ,. .. y m ) comprising all of the indicators of said set of indicators Y except each said indicator y j and by said exogenous data set X; for each indicator y j of said set of indicators Y, calculating a corresponding estimator ŷ j by projecting said indicator y j using a regression technique onto said projection space E (j) =σ(Y (j) , X), thereby forming a set of estimators Ŷ=(ŷ 1 ,. .. , ŷ j ,. .. , ŷ m ) corresponding to said set of indicators Y=(y 1 ,. .. , y j ,. .. , y m ); and normalizing each estimator ŷ j as a function of a reference value for the corresponding indicator y j and of a difference between each said estimator ŷ j and said corresponding indicator y j to form a set of standardized values {tilde over (Y)}=({tilde over (y)} 1 ,. .. {tilde over (y)} j ,. .. , {tilde over (y)} m ).