range significa gamma.
Avrei bisogno di vedere le ricette per essere sicurissima, ma io da madrelingua e cuoca non vedo altra soluzione. Immagino che le dosi siano indicate come p.e. 1/2 - 1 tsp - questo e' un "range" di 1/2 tsp poiche' la differenza tra la dose massima e minima e' di 1/2 tsp.
Specie nella cucina americana, le misure - cucchiai e cucchiani - sono misure assolutamente standard e senza la possibilita' di interpretazione libera. Facendo una ricerca molto semplice su google trovo

1 US teaspoon = 4.92892159 milliliters

Infatti sono disponibili misure standare di tablespoon, teaspoon, e frazioni di essi, per poter essere piu' precisi possibili.





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Note added at 18 hrs (2010-12-25 02:52:51 GMT)
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See:
http://en.wikipedia.org/wiki/Teaspoon#Measure_of_volume
http://www.exploratorium.edu/cooking/convert/measurements.ht...
http://www.ez-calculators.com/measurement-conversion-calcula...

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Note added at 3 days21 hrs (2010-12-28 05:11:35 GMT)
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see for instance
http://alderwoodquilts.blogspot.com/2010/07/ramen-cabbage-sa...
where it says
The proportions are very forgiving. You can adjust them to taste. For that reason, I list a "range" of quantities for a lot of the ingredients.

and
http://www.food.com/recipe/ingrids-apple-cottage-pudding-437...
This is a very forgiving recipe. It can take a variety of apples and a range of quantities

http://themessyapron.blogspot.com/2010_06_01_archive.html
I’ve included a range of quantities of wasabi that I think is reasonable in the recipe below. To me, a little eye watering at the dinner table is all part of the show, but if that’s not your thing, use less wasabi and seek your thrills elsewhere.

Look at the recipes - you will see what they mean.