Dear Ian, The mtz was transformed from a cryo-EM mrc file by phenix.map_to_structure_factors, and it contains both label "F" and "F_ampl". When I do phenix.mtz.dump, the labels include H,K,L,F,PHIF,F_ampl,HLA,HLB,HLC,HLD. Smith On Sunday, November 15, 2015 11:03 PM, Ian Tickle wrote: Hi, I assume what you mean is "what is the difference between the column labelled 'F' and the one labelled 'F_ampl' ?" in your MTZ file.  Since MTZ column labels are effectively arbitrary and may be user-specified, that is clearly an impossible question to answer without knowing the history of your MTZ file. The column labelled 'SIGFP' would normally be the standard deviation of the 'FP' column (assuming there is such a column), though there's no absolute requirement that this be the case (it just makes life easier for everyone if it is!), so again it's impossible to say which amplitude column the SIGFP column is related to without knowing the history of your file. Bottom line is: you have not supplied sufficient information to make it possible to answer your question. Cheers -- Ian On 15 November 2015 at 02:27, Smith Lee <[email protected]> wrote: Dear All, For a mtz file, will you please introduce to me the difference between label "F" and label "F_ampl"? For the label "SIGFP", is it the deviation related to label "F" or label "F_ampl"? Smith