Read Field to get direct access to the field component for the column. Usually, Field is a field component maintained by the dataset. In some cases, however, Field is maintained directly by THTMLTableColumn, such as when the column represents a calculated field. Do not set the Field property unless the TField object is obtained from the dataset of the TDSTableProducer that uses this THTMLTableColumn object, or is a calculated field based on that dataset. 

Setting Field automatically updates the FieldName property. 

FieldName 

DataSet