gaps = sapply(indices, function(i) {
                if (predict_from >= 2)
-                       data$getSerie(i+1)[predict_from] - data$getSerie(i+1)[predict_from-1]
+                       data$getSerie(i)[predict_from] - data$getSerie(i)[predict_from-1]
                else
-                       head(data$getSerie(i+1),1) - tail(data$getSerie(i),1)
+                       head(data$getSerie(i),1) - tail(data$getSerie(i-1),1)
        })
        scal_product = weights * gaps
        norm_fact = sum( weights[!is.na(scal_product)] )
 
                ref_serie = c( data$getCenteredSerie( pred$getIndexInData(index)-1 ),
                        data$getCenteredSerie( pred$getIndexInData(index) ) )
                centered_series = rbind(
-                       data$getCenteredSeries( pred$getParams(index)$indices ),
-                       data$getCenteredSeries( pred$getParams(index)$indices+1 ) )
+                       data$getCenteredSeries( pred$getParams(index)$indices-1 ),
+                       data$getCenteredSeries( pred$getParams(index)$indices ) )
                yrange = range( ref_serie,
                        quantile(centered_series, probs=c(0.025,0.975), na.rm=TRUE) )
                par(mar=c(4.7,5,1,1), cex.axis=1.5, cex.lab=1.5, lwd=2)