Hydrology Mass Balance Check

[Grace]

Hello, 

Before calibrating my model, one of the first steps was to check the hydrology mass balance. 

I looked at
Precipitation  = Prec + ET + RO + Lat_flow

I am assuming % error is the difference between ( PRCP  - Diff)/ (PRCP)

If so, is a 1.38% error applicable? Are there any papers that describe what they considered during their mass balance?