02.01 – Universal Design Layout Principles

FAST 2.01-01 Each column should have a single and consistent purpose

Constants (for example IRRs) should be clearly separated from series line items. Further requirements to provide section heading indenting, display totals, units, and an empty column to represent the period before modeling begins, should be placed in dedicated columns of appropriate width, a width that should be identical across all sheets in the model.

Exclusive use of a given column for a specific purpose not only improves clarity and structure, but can yield additional advantages. For instance, navigating through column A (say) for main section headings is facilitated with CTRL+ UP ARROW / DOWN ARROW when this column is not cluttered with other data. A separate units column causes the question of units to be begged, never a bad thing.

FAST 2.01-02 Series worksheets should be defined for a single time axis only

FAST-2.01-02.1 except series inputs sheets to avoid too many sheets

FAST-2.01-02.2 except where local exceptions warranted

Including more than one time axis on a given sheet must be carefully considered with reference to the four FAST principles. Making life easier on the modeler is insufficient justification. Every sheet should have a dominant time axis located within the freeze pane intersection for consistent viewability. Any other time axis used on the sheet should be clearly marked as an ‘alien’ time axis.

The standard formatting for ‘alien’ time axes will be described in Appendix A: FAST Formatting, page 43, in later version of this document.

FAST 2.01-03 Make only two columns matter

On the presumption that a series line item will be constructed via consistent formulas across the row, the requirement for model review is limited to confirming only that the first cell in the range is logically sensible. Therefore, only the constants column and the first series column tell the story.

FAST 2.01-04 Calculation logic should generally flow from top to bottom and left to right

This helps ensures logical flow and consistency of reading / calculation order.

FAST 2.01-05 Mark intra-sheet counter-flows with gray shade

Keeping with the ‘reading order equals calculation order’ design approach, logic should flow top-to-bottom on a given sheet, with necessary exceptions to this (counter-flows) kept to a minimum and clearly marked.

FAST 2.01-06 Limit counter-flows to opening balance positions

Although it often impossible to avoid counter-flows, having too many in a given section may be a sign that calculation section ordering may need to be considered.

Counter-flowing opening balance positions is generally considered benign since the opening balance is always linked to the previous period closing balance, so it is an indirect link to a previous period balance and thus in keeping with the ‘left to right, top to bottom’ rule ( FAST 2.01-04: Calculation logic should generally flow from top to bottom and left to right, above).

Counter-flowing closing balances are more problematic and highly likely to cause a circularity in the model either immediately, or eventually. FAST 1.01-11: Never release a model with purposeful use of circularity, page 14, discusses this further.

FAST 2.01-07 Present information horizontally

FAST-2.01-07.1 except for short vertical series for scenario structuring

FAST-2.01-07.2 except where vertical layout is more clear for printing

Vertical presentation should generally only be used when schedules are required for presentation / printing or where input structures are best laid out this way to support ’single column’ scenario loading or ‘picking’.

FAST 2.01-08 Do not hide anything

Rows, columns, and sheets themselves should rarely be hidden (a prohibition which generally includes use of Excel’s outline feature.

FAST-2.01-08.1 except for undefined time which should be hidden

The primary exception to the previous rule, and a strong design imperative, is to hide commercially undefined cell ranges (columns beyond the defined time axis on horizontal presentations).

Columns to the right that are beyond the sheets’ modeling range (to assist in CTRL+RIGHT ARROW operations), to restrict the x-axis on Excel charts, and in limited circumstances when the visible range of values is commercially uninteresting (for example first 15 columns are currently all zero).