Measure the pieces according to the volume of your serving glass. When a drink requires “parts”, it refers to the proportion of ingredients within the cocktail. Measuring a cocktail correctly is extremely important. Be scarce on one ingredient or pour another too much and you'll end up with an imperfect and inconsistent cocktail.
If the recipe calls for an ounce, it means an ounce, not anything like an ounce. The most important thing to remember when measuring alcohol is to fill up the meter, to really fill it up. The shaker must be so full that the liquid forms a convex arc, commonly known as a meniscus. Master this technique and you're about to become a master beverage maker.
I have seen more than a few waiters worry on the Internet about whether there is any way to protect their cocktails and other creations from use (or misuse). If you want to impress your friends and family by making great cocktails, understand the amount of alcohol in a drink, use measuring tools and use your judgment to determine when a drink tastes good. Preparing a cocktail properly can be as simple as you'd like, but to prepare drinks worthy of a cocktail bar, the devil is in the details. The other detail to consider is whether or not the scrambled cocktail is served as a martini or as a Negroni, some cocktails benefit from a higher water content or dilution than others.
A named cocktail may be a registered trademark, which may offer some control over how it is used, but it does not necessarily prevent its use. These are mixed drinks such as Scotch whiskey with soft drinks or gin-tonics, along with many champagne and sparkling wine cocktails. The main difference between shaking and shaking is that scrambled cocktails should receive as little aeration as possible to obtain a silky, semi-viscous elixir; generally, this means that all the ingredients in the shaken cocktail are transparent and free of the particles found in citrus juices, etc. Gently shaking the drink with ice prevents the cocktail from being over-diluted and keeps aeration to a minimum.
If the cocktail is served with ice, shake it vigorously for 5 to 7 seconds to let it air out and cool without achieving full dilution. The only case in which a trademark on a cocktail can be firmly enforced is when the trademark on the cocktail is the property of a brand. The difference between shaking and stirring may seem trivial, like one more step in a recipe that can be made with whatever you want, but mixing correctly is often the most important part of preparing a cocktail. This is one of the few recent cases in which a bar has been so dramatically affected by infringing a trademark cocktail.