Usefulness is a judgement about how relevant or helpful a particular source is in providing information about your topic.

The measure of a source's usefulness is based upon the question being asked of it.

If a source provides any information about the specific topic you're investigating, it is considered to be a useful source. 

Since a source's usefulness is based primarily upon its ability to provide valuable information on your topic, there are four different ways to prove that a source is useful:

 The academic article by American Egyptologist, Jones, is particularly useful in understanding how Egyptian temple inscriptions were used as political propaganda because he states that  “the extensive military conquests adorning the inner walls were meant to impress visitors with the pharaoh’s power and influence” (Jones, 1984, 45).

Pliny’s account is very useful in understanding public entertainment in Roman society and Roman attitudes towards gladiators since he states that he "visited the games many times" during his life (Agricola, VI.4).

The photograph is extremely useful in understanding the bombing of Hiroshima in 1945 because it clearly shows the destructive effects of the blast just weeks after the event.

Source A is very useful in understanding the experiences of Australian troops at Gallipoli because it is a letter was written by John Smith, an Australian soldier, which describes his personal experience of the Gallipoli landing on the 25th April 1915. Specifically, it explains how he and his fellow soldiers were overcome by fear and confusion due to a lack of communication from their officers. This is evident when he says in the letter that “I forgot all of my training and I began running like hell for safety”. Therefore, Source A provides first-hand account of the Gallipoli landings and is extremely useful in understanding the experiences of Australian troops during the event.

The plaster casts of the people who died at Pompeii in AD 79 shown in Sources G are extremely useful in the study of Pompeii. Even though the casts themselves were made during the mid-nineteenth century Italian archaeologist Fiorelli, they provide a rare insight into the position of the bodies at the time of death. However, both Smith, and Lazer provide an important explanation that there are problems in fully understanding the context of the individual casts. They both point out that the plaster casts and other skeletal remains have been frequently moved from their place of discovery. Smith highlights that due to “mobility of both casts and human skeletal remains”, it has lead to “mythologising” about individual people from the past (Source H). In a similar way, Lazer says that “many skeletons have been destroyed or removed from the site”, which makes accurate interpretations of the finds difficult (Source I). As a result, both the physical remains from Pompeii and the academic explanations provided in Sources G, H and I are very relevant to the study of ancient Pompeii.