Data quality checking can be done through various means, including:
At point of data entry, the software can check the data entered to see if it falls within the min-max ranges of that data element (based on all previous data registered).
Defining various validation rules, which can be run once the user has finished data entry. The user can also check the entered data for a particular period and Organization Unit(s) against the validation rules, and display the violations for these validation rules.
Analysis of data sets, ie. examining gaps in data.
Data triangulation which is comparing the same data or indicator from different sources.