It is an analog clock application that can also display a pendulum clock.
There are no ads at all.

Clock
Changeable clock position and size.
- Indigo Blue Clock - Second hand ticks away the time
- White Clock - Second hand moves smoothly
- Pendulum Clock - Pendulum ticks away the time
- Custom Clock - You can customize the clock yourself
(Multiple custom clocks available)

Background Image
Changeable background image position and size.
- Single Color - You can customize the color
- 10 preset background images
- Select background photo from photo library

Other features
- Status bar display switch
- Automatic sleep suppression
- Smooth Display selection (trade-off with battery consumption)
- Enlarging the background image (displayed on the whole screen)
- Digital time display
- Widget display (also supports iOS14)
- Support Dark Mode of iOS13

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There is also a free version of this app, "Analog Clock Lite - Pendulum" (with ads, with some functional restrictions).
You can also check the function there.