There's really no set measurements, it's all to your taste and creativity. All I can give you is the basic directions. Even if you this as is, I promise, it will become one of your favorite meals. But, you can add other ingredients: red wine, crushed tomatoes, potatoes, carrots. Make it your own and enjoy your creation!
Sprinkle eye round with granulated garlic and black pepper; brown in skillet on medium high, on all sides. (Cover it, or it will splatter all over your nice clean stove.) Place roast in your slow cooker, set on low. If you don't have the time to brown it, that's okay too. Just season and place in your slow cooker, then pour the onion soup over it.
Pour soup into the pan and heat just enough to loosen all the goodness of the meat drippings into the soup. Then, pour over the roast in the slow cooker. (If you're roasting it in the oven, it's 350'F. for about 2 hours.)
Cover and cook on low approx. 5 hours (well done) or your preference, rare, medium or well done.
When done, take out and let it rest before cutting. Use the juice as is, or strain into a pan and make a rich brown gravy, or use juice as is. Great either way.