In the last chapter you created two very simple calculation fields using numbers: Extended Price and Invoice Total. But those calculations were very simple. Now, you build on those basic concepts to see how you can make a set of calculations that fit an upcoming sales promotion.
10.2.1. Preparing the Data
You've decided to start reselling personal security products to your customers. To help you keep track of things, you need to add a Products table to your database. The table should have these fields:
Note: See Section 7.3 for advice on creating tables.
Once you've defined this new table, FileMaker automatically creates a layoutProducts. Switch to that layout now and create a few product records. To help drive sales to your larger clients, you want to implement a volume discount schemethey should get a 5 percent discount if they buy enough. But some of the products you sell don't have enough markup to justify these discounts. You want to be sure the discount never reduces your markup below 20 percent.
First, you add a line to your marketing materials: "Volume discounts not available for all products." You can make this line as small as humanly possible and hide it way down in the corner. Next, you need to fix your database so it tells you the discount price for each product.
10.2.2. Building the Calculation Fields
To implement this discount scheme, take what you need to know and translate it into calculation terms. You need three fields to carry out your sales promotion logic.
Price Each * .95
Cost * 1.2
Max ( Price Each * .95 ; Cost * 1.2 )
Using the Max function, the previous calculation results in either the discounted price, or the minimum price, whichever is greater (see the box on Section 10.2.3). That result's almost perfect. But suppose you have a product whose normal price is less than 20 percent above cost (hey, it's a competitive market). If you use the Max calculation as it is now, the new discounted price is more than the normal price. You need to go back and add to your calculation so that it takes the regular price into account, and uses that price if it's lower than the calculated discount. Read on to learn how to think through this calculation quandary.
UP TO SPEED The Max and Min Functions 
Many times, you need to know either the highest or lowest value in a series. The Max function and its twin sister, Min, fulfill these needs and you find them in the function list's Aggregate functions category. Like all the aggregate functions, they expect at least one parameter, and are glad to get more. Every parameter should be a number. Your parameters can be:
The Max function looks at every number referenced and returns whichever is largest. Min, on the other hand, returns the smallest value. For example, look at this calculation: Max ( 10 ; 3 ; 72 ; 19 ; 1 ) Its result is 72, since that's the largest of the parameters. If you had a repeating field called Distances that held the distances from your office to each Krispy Kreme store, you could use this calculation to find the closest sugar fix: Min ( Distances ) The same is true for related fields too. This calculation finds the most expensive line item: Max ( Line Items::Price ) For another example of an aggregate function, Sum, see Section 9.1.1. 
10.2.3. Constructing the Calculation
When calculations start to get complicated like this discount price example, imagine that you have a field that contains the value you already want. You can use this pretend field in your new calculation, and then, when you're all finished, put the old calculation in place of the pretend field. In this case, just pretend you have a field called Calculated Discount that holds the discount price. With that imaginary field in mind, you can fix your problem with this calculation:
Min ( Calculated Discount ; Price Each )
The result of this calculation is either the calculated discount or the regular price, if it's lower. Now, just put the old calculation in place of the words "Calculated Discount" (since the old calculation results in the calculated discount):
Min ( Max ( Price Each * .95 ; Cost * 1.2 ) ; Price Each )
The entire Max function, complete with its two parameters, is now the Min function's first parameter. You might think it looks a little confusing at first, but with practice you become accustomed to looking at functionsinsidefunctions like this.
If it helps, you can add white space and comments to clarify the calculation, as Figure 102 shows.

To use the calculation, just create a new calculation field (call it Discounted Price) with the calculation above. It automatically adjusts and shows you an appropriate discounted price.
If you want to test a complicated calculation, spotcheck a few records where you know the result. Sometimes the math is so complex that you just have to work it out on paper and enter dummy records to check the calculation. Usually, if a calculation isn't working, you can figure out how to fix it when you compare your math to the value in the field.
Part I: Introduction to FileMaker Pro
Your First Database
Organizing and Editing Records
Building a New Database
Part II: Layout Basics
Layout Basics
Creating Layouts
Advanced Layouts and Reports
Part III: Multiple Tables and Relationships
Multiple Tables and Relationships
Advanced Relationship Techniques
Part IV: Calculations
Introduction to Calculations
Calculations and Data Types
Advanced Calculations
Extending Calculations
Part V: Scripting
Scripting Basics
Script Steps
Advanced Scripting
Part VI: Security and Integration
Security
Exporting and Importing
Sharing Your Database
Developer Utilities
Part VII: Appendixes
Appendix A. Getting Help