The Clock menu in the center of the top panel when clicked will show the Calendar and the upcoming events from the Evolution application. On the bottom two buttons allow to open the Date and Time Settings and the calendar application.
The right area of the panel will offer place for the a11y, Volume and User menus.
The a11y menu contains a lot of features to assist users with usage or sight difficulties. Every option can be simply enabled or disabled with the switches inside the menu. Their function should be self descriptive but further details can be found opening the Universal Access Settings dialog.
The Volume menu offers only a slider for the global volume so that every playing applications will be affected by its change.
The global volume slider shouldn’t be moved over the point shown in the image behind. The remaining level on the right does audio boost, resulting in louder but distorted sound if not well balanced.
At first sight is not simple to acknowledge where the normal maximum volume (100%) is reached and where the audio is extra amplified. Moreover the slider controls only the global (Master channel) volume for every audio source, it cannot control single applications audio levels. The Sound Settings dialog needs to be opened to adjust such settings.
The uppermost slider controls the global audio volume, exactly like that in the Volume menu, and shows clearly where the 100% unboosted audio volume is reached.
If there are running applications playing sounds their volume level can be adjusted in the Applications tab. In the above image two applications are currently playing audio with different volume settings.
Further information can be found in: GNOME Shell Design.