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Build the early estimate from area rates or from comparable completed work, and record with it the scope assumed, the price level used and what is excluded. Carry that figure as the amount put up for approval.

เหตุผล: The approved amount is fixed from this estimate and governs the job for years, so its assumptions matter more than its precision. An estimate that states what it left out can be revised for a stated reason; one that states only a number is revised for what looks like a mistake.

Measure and price the work in full on the governing schedule, then set the total beside the approved amount and account for the difference sub-head by sub-head rather than as one variance.

เหตุผล: The gap between a preliminary and a detailed estimate is normal and is expected to be explained. Explaining it by sub-head shows whether the scope grew, the rates moved or the early estimate was thin, and only the first of those is a reason to revise the approval.

Hold the contingency as its own provision inside the sanctioned amount, with a note of what it is for, and record each drawing on it against the event that caused it.

เหตุผล: Contingency spread into rates is spent invisibly and is gone before anyone knows it was being used. Held apart, it answers the only question that matters halfway through a job, which is how much room is left before the ceiling and what has already consumed the rest.

Record every deviation with its value, whether it is an excess over a sanctioned quantity, a new item or a saving, and keep the cumulative effect against the sanctioned amount rather than against the last approved change.

เหตุผล: Deviations are approved one at a time and consume the ceiling collectively, which is precisely the arithmetic nobody does in the moment. A running total is the only instrument that turns twelve reasonable individual decisions into a visible position.

Report the position against the sanctioned amount at each period, and when the trend shows the ceiling being reached, produce the revised estimate with the reasons separated into scope, quantity and rate, and put it up while there is still room to work under the existing sanction.

เหตุผล: A revision sought early is a technical submission with an answer to every question. One sought after the ceiling is passed is the same submission with an explanation attached for why work continued, and that explanation is what turns an ordinary cost increase into a finding against the department.