How do I evaluate the usefulness of a source?

When I look at a source, the technique I use to answer these types of questions is DAPAL, which stands for:Date - When was this written - was it written immediately after the event or years later? Author - Is it a first hand account (by a person who was present at the event) or a secondary account (written by someone who wasn't there)? What is the author's background - a professor or journalist or soldier etc. Purpose - Is it a personal account or is it trying to send a specific message? Is it propaganda? Is it trying to be informative or is it an opinion piece?Accuracy - Does it omit significant info about the event? Is it wrong with some facts? What does the content tell us? Limitations - Is the source biased in any way - is it from an untrustworthy source, or can only tell us one perspective?By going through the source point by point, I can see whether the source is useful, and so can construct my answer. It is important to remember that all sources are useful in some way - even a heavily biased source reveals something about attitudes held by society at the time. But every source, no matter how reliable it may seem, cannot tell the whole story. The answer is never just 'no' or 'yes'.