Row numbers in master/detail reports work the same as in regular lists. But there is one difference. If the data band details use numbering, each sublist has its own numbering. For example, the image below shows a master-detail report.

Numbering in the master list is displayed in red. Numbering to the detail list is shown in green. As shown, numbering into the detail list starts every time after printing a line from the master list.

In addition to using system variables, numbering can also be done using the Line property of the data band. The expression in this case is as follows.

{DetailDataBand1.Line}.{Customers.CompanyName}

why do you need it? Why not use Line's system variables? A system variable has a visibility zone. For example, let's say you use the Line system variable for your master band. In this case, numbering is output on the master band. If the Line system variable is used for the detail band, then the detail band numbering is printed in this case. But what if we need to output the numbering of two different data bands in one expression? In this case, use the Line property of the data band. For example, see the formula below for the detail band.

{DataBand1.Line}.{Line}.{Products.ProductName}

This will give you the following results in your report: