Custom field in VA01 at item level in Additional Data B Tab

Hi ,

I have a requirement to add a custom field at item level in Additional Data B tab of VA01/VA02. We have to store the data in that field in the VBAP table also have to validate the data entered in the field when user hit save.

Can any body tell me step by step procedure to do that.

Appreciate your response.

Thanks,

Rohit