It's nice to have a clock where you can see it while riding, since it's not possible to see your watch when ATGATT. Here's my solution.
I glue the watch to the tach face with Liquid Nails Home Projects Repair Adhesive http://www.liquidnails.com/products/product.jsp?productId=78#details. It won't etch the plastic face, and holds really well. On my GS750, I had a watch mounted to the Quicksilver fairing, and when the front tire went flat on the freeway, I lost the front and innards of the watch, but the back was still in place. If you pry slowly with a thin edge, like a putty knife, the watch will come off fairly easily, since the adhesive has relatively low peel strength.
I glue the watch to the tach face with Liquid Nails Home Projects Repair Adhesive http://www.liquidnails.com/products/product.jsp?productId=78#details. It won't etch the plastic face, and holds really well. On my GS750, I had a watch mounted to the Quicksilver fairing, and when the front tire went flat on the freeway, I lost the front and innards of the watch, but the back was still in place. If you pry slowly with a thin edge, like a putty knife, the watch will come off fairly easily, since the adhesive has relatively low peel strength.