Key Unit Concepts

Understanding Units

Calculation Consistency

Units allow you to ensure that Calculations are consistent.

As a simple example, it is logically incorrect to sum together two Variables which have a different unit.

Adding a Variable in GBP to a Variable in USD has no real meaning. If you attempt to do this, Models will warn you that it cannot determine the resulting Unit, which will prompt you to correct the Calculation. One of the two Variables should first be converted to the other currency, before summing, using an exchange rate Variable, with Unit GBP/USD or vice versa.

Non-additive operations, such as multiplication, transform Units.

Multiplying an exchange rate with Unit GBP/USD by a Variable with Unit USD results in a Variable with Unit GBP.

Squaring a Variable will raise the Unit to a power of 2: e.g., Distance in metre multiplied by itself will result in a Variable with Unit metre^2

Models will automatically derive the Units of your Calculations and tell you the resulting Unit, or display a warning if the Unit is not as expected.

Units and Tags

Just like Dimensions and other Taglo concepts, Units are based on Tags. Each Unit component (e.g. GBP, USD, metre) is itself an Abstract Tag.

When you create a new type of Unit, you simply create a new Abstract Tag.

Use the Short Name property of a Tag to determine how the Tag will be displayed within a Unit (e.g., the metre Tag has a Short Name of m).

Commonly used Units like currencies, units of time, and units of distance can be found in the built-in Namespaces.

Inheritance

Unit inheritance analysis is available from Version 0.1.4.0 of Models

Because Units are based on Tags, they have access to all of the relationships you have created between Tags. This allows Models to make more intelligent inferences about the output Unit of a Calculation.

For instance, if you have a Variable with Unit Apple, and a second Variable with Unit Banana, you should not ordinarily sum these Variables together, as explained above, and Models will warn you about it if you do.

However, if the Apple and Banana Tags both have a third tag, Fruit as a common parent Tag, Models can infer that the Calculation is adding Fruit together, rather than Apples and Bananas, resulting in an output Unit of Fruit.

The above example will be represented in the Variable view as in the screenshot below. When a Variable is reliant on inheritance to calculate or correctly match its Unit, as is the case for Total Fruit below, Models will show a warning (1), in the Variable.

Unit inheritance example

Disabling Inheritance

Unit inheritance can be enabled/disabled in the Model settings wizard, as shown below. Open the settings wizard from the Model Settings bar, and select or deselect the Allow Unit inheritance option (1) as required.

The Allow Unit Inheritance setting

Compound Units

Many Units are Compound Units: for example, the exchange rate GBP/USD. In Taglo, we refer to each component of the Unit as a Unit Part.

In this example, the USD Unit Part has an Order of -1, making it the denominator of the Unit.

In the next section, Advanced Units, you will learn how editing each Unit Part adds functionality to Taglo software.

Summary

Units help you achieve logical consistency in your calculations. Models allows you to add extra time and contextual detail to your Units, which provide useful information about how the Variables and Assumptions in your Model should be treated.

As you read more about working in Models, you will see how these concepts are used to enable powerful functionality.

For instance, Dimensions work by automatically applying context Tags to the underlying Unit of a Variable.

Read on to learn how to create Units.