Move a number only when a reason moves with it

The fastest way to lose trust in a forecast is to let numbers drift without explanation, so this month's figure differs from last month's and nobody can say why. Every change should carry its cause: a variation agreed at a figure, a contra accepted, a claim conceded, a rate proven on site. With the reasons attached, the forecast is a running record of what happened to the account; without them, a number nobody believes.