Need Information about the Causal Factor 'Trend' and it's Values for Planning Central

Summary:

We are implementing the Demand Plan in Planning Central.

For Demand Planning in Planning Central, 'Trend' is one of the seeded Causal Factors.

Document: How To Use Causal Factors In Planning Central Demand Plan ? (Doc ID 2405184.1)

Explains :

Trend - For 'Trend for Forecast' ,value is 1 for the beginning period of casual data and increments by 1 until last period . This linear trend is compared with trend in historical data to calculate factors for Trend which will be used in future while forecasting

We need to understand how the 'Trend' causal factor Entry works ?

Why the Value for 'Trend' goes on increasing by 1 from beginning of period until the last period?