The binding legal principles established are: (1) Under clause 2(8) of the COLTO contract, the employer has the power to reverse (revoke or annul) any certificate issued by the engineer, and if deemed necessary, to amend it, with such amended certificate deemed to be issued by the engineer. (2) The manner in which the reversal is effected (whether the employer issues a new certificate itself or instructs the engineer to recalculate) does not affect the validity of the exercise of the power under clause 2(8). (3) The power to reverse certificates under a clause beginning "Notwithstanding any provisions to the contrary in the Contract" and referring to "any certificate" extends to all certificates, including those embodying the engineer's rulings under claims provisions (such as clause 51), unless expressly limited. (4) A certificate issued after cancellation of the contract is not a certificate contemplated by the contract while in force. (5) Where a contractor purports to cancel a contract under a specific contractual provision (clause 59) for employer's default, but the employer was not in fact in default and accepts the contractor's conduct as repudiation, the cancellation is not effected under that contractual provision and the contractor cannot rely on survival clauses attached to that provision. (6) The contractor is not without remedy where the employer reverses certificates, as dispute resolution provisions in the contract (clauses 60 and 61) provide mechanisms for resolution.