Hardcoded input
AccountingA number typed directly inside a formula rather than referenced from a labelled input cell, so the choice is invisible to anyone reading the model.
Also written: hardcode, hardcoded, hard coded number
Typed numbers are exactly what belongs in the input area of a model, where a reader knows to look for them. The problem is a number typed inside a calculation, where nobody can see that a choice was made without clicking into the cell.
The damage is not the number itself, which may well be right. It is that the model stops responding to the assumption it appears to be using. Update the tax rate in the input block and the hardcoded one keeps running at the old figure, and a sensitivity table built on top will flex an input that part of the model no longer listens to.
Colour coding is the usual defence, blue for typed inputs and black for formulas, with the exact palette varying by firm. It works because it makes the violation visible rather than because it prevents it.
In a marked exercise it costs more than an arithmetic slip. Graders check whether a cell is a live formula and whether it references the cells it should, on the reasoning that a right answer produced by typing a constant demonstrates nothing about method.
The everyday test is whether someone else could change every assumption in the model without opening a single formula. If not, something is buried.
Worked example
A model computes tax as profit before tax multiplied by 0.25, with the 25 typed into the formula, while the assumptions block also shows a tax rate of 25%.
Someone runs the case at 28% by changing the assumptions block. Nothing moves. The model reports a tax charge that contradicts its own stated assumption, and the only clue is inside a formula nobody has reason to open.