Amount Type parameter in Trial Balance Report

Can some one explain the working logic of the parameter 'Amount Type' in Trial Balance Report.

I could see the list of values of the paramater are YTD and PTD.

If i select PTD does it show only the period activity, ignoring the previos balance of the account and in the same fashion, if i select YTD, does it show only activity of that year ignoring the previous years balance.

Request you to throw some light.