Tabular editor syntax chart datalabels

hello,

I'm new to Power Bi and Tabular editor. 

I have created a graph which plots the historical value of a parameter. each value corresponds to an event (called EVENT_TYPE)

I want to replace current datalabels with event type name on the graph.

Note that I have a table containing historical values of the parameter calld : HISTORICAL. Waht is the syntax to write in tabular editor calculation item to show the vent type.

Thanks in advance 🙂