Often coverage maps show general coverage for large regions and therefore any boundary indicated should not be interpreted as a rigid limit. The biggest cause of uncertainty for a coverage map is the quality (mainly sensitivity) of receiving apparatus used. A coverage map may be produced to indicate the area in which a certain signal strength is delivered. Even if it is 100% accurate (which it never is), a major factor on whether a signal is receivable depends very much on whether the receiving apparatus is sensitive enough to use a signal of that level. Commercial receivers can vary widely in their sensitivity, thus perception of coverage can vary widely.