Calendar Formating button

Hello Everyone:

I have a little problem with one of the users. In the calendar view everybody else has a button label formatting that allows the user to switch between summary and normal calendar view but for this client that button is missing!!!

He is using a small screen with high resolution but I could not find any information on how to hide or unhide that button. Does anybody knows how this gets done? or why he may not have that button? Any ideas will be great.

Thanks