Painstakingly means doing something in a very careful, thorough way — slowly, and with attention to small things. It is the adverb that belongs with painstaking. You put it with a verb: she painstakingly checked each number; he painstakingly copied the drawing. It often suggests that the job was long, and that rushing would have spoiled it. Like painstaking, it is a little formal, and it still has nothing to do with physical pain. In easy talk, really carefully or bit by bit will often do the same job.