Where work can be described and given in items in accordance with the tabulated rules of measurement but the quantity of work cannot be accurately determined, an estimate of the quantity shall be given and identified as a ‘provisional quantity’. Work items identified as a ‘provisional quantity’ shall be subject to remeasurement when they have been completed. The ‘approximate quantity’ shall be substituted by the ‘firm quantity’ measured, and the total price for that item adjusted to reflect the change in quantity. Where the variance between the ‘provisional quantity’ and the ‘firm quantity’ measured is less than 20 per cent, the rate tendered by the contractor shall not be subject to review. Where the variance is significant (i.e. 20 per cent or more), the rate can be reviewed to ensure that the rate is fair and reasonable to both the employer and contractor.