How is Sales PTD is calculated in R42611

Hi there ,

I'm have been trying to understand the difference between Sales YTD and Sales PTD in the R42611 report. I know the Sales YTD is the sum of all sales of one item from the beginning of the fiscal year to date is stored in F4229 as CYS.

To have a close look at these two figures I have set the period in the processing option to match the fiscal year and ran the report R42611. I was naturally expecting the sum of these figures to be exactly the same as their dates correspond but I surprisingly realized that the Sales PTD is less than the Sale YTD. Can anyone tell me how the Sales Period To Date (PTD) is calculated? Looking into the ER of R42611 does not show how it is calculated.