In History, primary sources are objects and documents created or written during the time being investigated, for example during an event or very soon after it. Examples of primary sources include official documents, such as laws and treaties; personal documents, such as diaries and letters; photographs; film and documentaries. These original, first-hand accounts are analysed by the historian to answer questions about the past. A primary source can also be unprocessed, original materials collected by the students, for example, field notes from observations, measurements taken from experiments, or responses received from a survey or questionnaire.