This function basically corresponds to the mapping function LookupGlobalValue. However, LookupTPValue specifies a table (LookupTable) and not just a global table type.
LookupTPValue('Tabelle','Key','Description')
LookupTPValue('Tabelle','Key')
LookupTPValue('Sizes',@Ean,'Ean Calida')
LookupTPValue('Sizes',@Ean)