For each calculation and script created in LiveCycle Designer ES, you must specify the location where you want the calculation or script to run.
Unless you are using server-based processing such as LiveCycle Forms ES, you should ensure that all of your calculations and scripts are set to run on the client application (for example, on Acrobat or a web browser).
If you are using server-based processing, you can choose between running calculations on the client application, or running them on the server. By choosing to have calculations and scripts run on the server, you are choosing to run the scripts at a specific point during the form-rendering process. For more information, see Creating scripts for use with LiveCycle Forms ES.
If you choose Client And Server from the Run At list, your calculation or script is available to both client and server-based applications. This option is useful, for example, if you do not know whether your users will have client or server applications when they attempt to use your form. It is also useful if you want certain form objects to behave one way to a client application and another to a server-based application.
See also 

Determining where to run your calculation or script