Historians make distinctions between what they call primary sources and secondary sources. Primary sources are firsthand accounts of events, recorded or produced by witnesses or recorders who were present at the time of the event or experienced the conditions being documented. Primary sources are characterized by their content, regardless of whether they are available in original, microfilm/microfiche, digital format, or published format. Historians carefully read and evaluate primary sources to make decisions about how and why things happened as they did.