In many experiments, we end up comparing two values - an experimental value with a theoretical value, my value with the "accepted value", two experimental values, whatever. To compare the values, we compare ranges. Sooner or later it occurs to beginning physicists that they can make all of their experiments "work" every time just by making the ranges big enough - that is, if the precision of the measurements is low enough, you can call just about any two values "possibly equal"! Instant Accuracy!
This is just not the way science should be done, folks! We need to claim as much precision as we can justify - this is the only way that science can make progress. If there is a discrepancy between values in our experiment, so be it! As scientists, it is our solemn duty to try to figure out what is going on.
We have already discussed factors that can affect the precision of a measurement. There are also several places to look for factors affecting the accuracy of your results: