It's just like algebra:
1 1/2 X + 1/2 X + 2 X =4 X
Substitute X for your favorite measure, be it ounce, jigger, cl, ml, quart or
gallon and the recipe will be right, if too big or too small. In the above
example, let's make a bad kamikazee: (I chose the above equation at random so
I'm just plugging in a 3 ingredient drink. The proportions are very wrong)
1 1/2 OZ vodka
1/2 OZ Triple
2 OZ Roses Lime
To translate this into "parts", it looks like 1/2 oz is our base measure (It
easily divides into the other 2 ingredients). SO to see the above "recipe" as
a proportional recipe:
3 parts Vodka
1 part Triple
4 parts Roses
So to follow this recipe on a grand scale, like for large pary batches, you
could do:
3 bottles vodka
1 bottle Triple
4 bottles Roses
(Substitute Cases for Bottles if your party is particularly large. Following
this recipe will garuntee it won't be)
Notice, also, that the total number of parts is 8. Now this is convenient for
me because I know my martini glasses hold an 8 count, the way I pour. So for
a bad Kamikazee Straight Up, I'd do a 3 count of vodka, 1 count of triple, 4
count of roses. Boom! fits the glass like a glove.