At Mitxels.com he offers a precision clock kit based on GPS. It has large red LED displays and, once built, is very impressive. The only lees than spectacular aspect of the kit is mounting it to a wall. It has two holes, one at each end. Most temporary and even permanent hooks will not clear the components on the back.
3d printing to the rescue. These brackets simply slid over the board and clear all of the components on the back of the clock. I use the 3M command hook tapes to secure the clock to the wall.