difference between original EEG.edf data from physionet.org and EEG data read using edfread.m

Hello, for analysing edf data of physionet.org I used function edfread from file exchange in mathwork. when I compare the original data (from https://www.physionet.org/cgi-bin/atm/ATM ) to edfread.m I see a little change. for example 0,06747539 (original data) changes to 0.064545662 using edfread.m. I want to know if this amount of change is important or not in classifiing EEG SLEEP data.

[dpb]

That looks like too large of a difference to not have an explanation to me, like you're not actually comparing the same points.

I know absolutely nothing about the format but I notice inside the function the data are encoded as integer w/ apparently some scaling; perhaps there's something going on with the latter as integer values should be identical.

The values are taken from the file as

tmpdata(recnum).data{ii} = fread(fid,hdr.samples(ii),'int16') * scalefac(ii) + dc(ii);

where the scalefactor and DC offset are computed from some header info.

I think I'd look at the input in the file more carefully before just proceeding here...