# Changing the offset of a data item of a Modbus RTU server

The offset specifies the address of the data to be accessed within a data block. The data block itself is specified by selecting the appropriate function code (e. g. FC 1 for reading Coils). The data addresses are defined by the manufacturer of the Modbus RTU device.

1. You must add a data item to the Modbus RTU server.

1. Open the device view.
2. In the device tree, double-click the server whose data item you want to edit.
3. Select the data item you want to change.
4. Double-click the text box Offset.
5. In the text box, enter a new offset value in either decimal format or hexadecimal format ( e. g. 163 or 0xA3).
6. Press Enter.