Measurements
The wikipedia article for the cup unit identifies two different measures used in the US: a legal cup of 240ml and a customary cup of ~236.588ml.
Similarly, the tablespoon and teaspoon articles describe traditional measures (~14.8ml and ~4.93ml respectively) and measures used in "nutritional labeling" (15ml and 5ml).
Are measuring spoons in the US calibrated to the traditional, or to the legal definitions of these units?
This is something that really puzzled me when I went living in an English-speaking country. Having grown up in Italy, where recipes tell you "Put 120g of this then add 250g of that", I've always used a scale. The first time I saw I recipe with cups and teaspoons I said: yeah, but I've got 10 types of cups in the kitchen... which one should I be using?
Then someone told me that they were real unit of measure and introduced me to measuring spoons (something that in Italy would be very difficult to come by).
So, going back to your question:
I strongly second @Adam's opinion of buying a digital scale: they're cheap and do the job (personally, I would not spend more than $30-40 on it, but you can find $300 ones if you wish).
If your recipe calls for teaspoons, cups, etc. then you can:
Buy measuring spoons/cups (you can find a complete set for $10, for instance this)
Convert them to g (or whatever your scale measures) using an online calculator. If you google for "teaspoons to grams" or "cups to grams" you'll find plenty.
You can even get an app on your phone. I use this app which works pretty well (I'm sure there's a similar thing for iPhone, but I don't use Apple products, so I can't help there).
The General Mills site has the image of the "original" pancake mix along with it's nutrition facts.
The serving size is 1/3 cup mix (40 g)
This means that one cup of the mix should weigh 120 g (4-1/4 oz).
Best Answer
Great question Chris! I'm a US baker who has been baking for a LONG time and never gave it any thought whether my measuring utensils are "legal" or "traditional" - they say "1 cup", "1 Tsp", "1 TBSP", etc.
In practice, all this has meant to me is that when my US recipes call for 1 cup of flour, I measure 1 level measuring cup of flour. Same for teaspoons and tablespoons. My European cookbooks refer to ingredients in weight (250 grams, for example). In those cases, I would either convert those measurements into my more familiar cups, tsp's, TBSP's, etc., or use another set of utensils with measurements marked on the side.
While I've used the written measurements for a guideline, I've always also depended on the preparation instructions to determine the correct consistency of the dough or batter. This is particularly true for flour and liquids.
Regarding uniformity in the measurement tools, unfortunately for the home cook, there is no one monopoly. Every grocery store, dollar store and cooking store has an assortment of measuring cups and spoons. Some of the better measuring cups, like those from Pyrex, have volumes written on the side of the cup to use as guides.