# TABULA/samples/indicator flag

This is SAMPLE7. To work with this sample, enter \$7

```indicator flag
┌ {1}    0 *   unit
└>{2}   NO     is {1} non-zero?
```

## Rationale

An indicator flag is a quantity which gets displayed as YES or NO instead of a value (1 or 0) followed by a units.

You can use it as a switch to modify the behavior of the t-table in some way.

## Try it out

1. Select line {1} then enter 0
Line {2} will change to NO.
2. Select line {1} then enter 1
Line {2} will change to YES.
3. Select line {1} then change its value to any non-zero number
Line {2} will remain unchanged at YES.
4. Select line {2} then enter YES
Line {1} will change to 1.

The indicator flag at line {2} has an underlying value which tracks the value of {1}.

• It displays NO whenever {2} has the value zero.
• Otherwise it displays YES.
• If you force {2} = YES, then {1} becomes 1 by backfitting.

## Build this t-table

1. Clear the t-table.
2. Edit the title to read: indicator flag
3. Make a new line {1}.
4. Make an equal line {2} equal to {1}.
5. Change the units of line {2} to [!]
6. Re-label line {2} to read: is {1} non-zero?