>
> In our history, a long list of doubles (64 Bit) fas followed by three floats (32 bit)
>

Padding trouble, mixing "double" and "float" trouble. Ouch.

Best wisdom I received on this: never use "float", always use "double".

I was burned by "float" with following code, which produced the same result from
analyzing 100 files as from analyzing 1000 files. (why did we take data for 10 weeks
instead of 1 week?). Hint: "float" overflows way too quickly, after overflow sum+=1 does not change
the value of "sum". The actual code used ROOT TH1F. Lesson: always use TH1D.

float sum = 0; // should always be "double" !!!
foreach data_file {
    foreach data from current data file {
        sum += data;
    }   
}
print sum;

K.O.