I'm trying to find out how RMA normalized signal intensity values in this sample have been calculated. I tried to perform RMA in R, but the results are different

library(affy)
cell_file = ReadAffy()
mat = exprs(cell_file)
exprs(affy::rma(cell_file))[1]

This code returns the value 11.79282 for the first probe (1007_s_at), but it should be 12.123249 according to the website.

I also asked the same question here

Exact OMCIS reproduction down to the values without code and software version is borderline impossible. Either use the values as provided or start with the CEL files and apply the established best practices. The latter is more reproducible, the former is easier. Choice is yours.