No, that won't work. Imagine you had values of 1,1,1,1 or 2,2,2,2, both would give you results of 0.
If you want to normalize the values, all you need to do is subtract the average over the time period, or just minus 800 for the quick and dirty version.
So for a single second at 256Hz, take the sum of all 256 values and divide it by 256. This will give you the average over the second (probably ~800uV). The to normalize each value, subtract this average from each individual value.
So if the value T0 is 825, you'd get 25., if T1 is 750, you'd get -50. etc. etc.