What's in a calculation?
The introduction to OAK's notion of reconstruction refers to it as applying to "a calculation". A calculation that is at all interesting and substantial will take more than one formula to conclude. At least, it should do. Certainly, the practice of Operis, and of well-trained analysts elsewhere, is to build up results using a sequence of several short formulas, since they are much easier to understand than a small number of long formulas. Trying to derive a result using a single formula that continues for many lines in the formula bar is considered a Bad Thing.
Applying OAK's Formula | Reconstruct command will therefore in many cases only tell a fragment of the story of a calculation. What is needed is to look not just at the formula in the chosen cells, but at the precedents of those cells, and their precedents too, possibly all the way back to the inputs.
OAK can be instructed to do exactly this. It will take a formula, for example =F7-F5; look at the formulas in those two cells, and substitute those into the formula, to get perhaps =F20*(1+F22) - (F30+F31). If these four cells in turn mention other cells, their contents will be substituted into the growing formula. Eventually, when the process stops, OAK will deliver a new workbook bearing the reconstruction report.
Since a formula commonly mentions more than one other cell, the result of substituting precedent formulas into a reconstruction can quickly become large due to fan-out. In practice, OAK can be allowed the freedom to reconstruct a calculation all the way back to its inputs only in rather simple models; otherwise, the reports become impracticably large and take a long time to generate.
Levels
The main way that the reconstruction can be controlled is by telling OAK how many levels of precedents to substitute.
•A level 0 reconstruction reconstructs a given formula, but does not do any substitution of precedents. The simple examples (here and here) used to introduce the concept of reconstruction show this basic level of reconstruction.
•A level 1 reconstruction takes a given formula, and then expands it by replacing the references to its precedent cells by their formulas. In the example above , =F20*(1+F22) - (F30+F31) was a level 1 reconstruction.
•A level 2 reconstruction is expanded to include its precedents' precedents.
The number of levels of precedent substitution that OAK is to make is specified in the dialog box that is presented by the Formula | Reconstruct command.
Low values here will produce a short reconstruction quickly. High values will produce take longer to produce a more elaborate reconstruction.