HP (Hewlett-Packard) HP 33s ユーザーズマニュアル

Those eight silver paint keys have their specific pressure points marked in blue 
position in the illustration below.   

To use those keys, make sure to press down the corresponding position for the 
desired function. 

One of the first things you need to know is how to clear: how to correct numbers, 
clear the display, or start over.