The Contractor offers to complete the whole of the work in the Contract Bills for the Contract Sum; in addition he offers to undertake variations at the prices entered into the Contract Bills. It is nonsense, therefore, to demand that these prices can be overturned and set aside on the one occasion for which they were designed. A variation should be a change reasonably and naturally occurring in the course of developing the design and in response to changes reasonably required by the Employer; not contrived in order to take advantage of an oversight. A variation omitting work can also have an impact on remaining work in that it may change the conditions under which that remaining work is executed, e.g. omitting a significant value of reinforcement could mean that the cost of the crane needed to move reinforcement around the site has to be recovered over a smaller quantity of work.