Process of nonogram solving can be much convenient and effective if a specially designed program used for that. You can easily check any of your assumptions, because you can undo all of your moves. You can see if a row or a column is completed. Helpful tooltips show you status for a cell under cursor, so you should not check header of the cell's row.

The offline version is much faster and more powerful than online version, on the other hand - online version is more convenient, doesn't require installation and contains free nonograms to solve.