Once a contract has been established between two parties, does not necessarily mean that its provisions are clear and beyond dispute. The parties may have differing views as to what was expressly agreed upon, and may encounter potential ambiguity and difficultly in coming to an understanding to the terms upon which they have agreed to. Furthermore, a contract may not simply consist of express terms either spoken, or in a signed written document, or in an unsigned written document. It may have been entered into against a background of custom ....