grammaticality - Is it "a uniform" or "an uniform"?

On a Physics specification, it says:

6.7 Know how to use two permanent magnets to produce a uniform magnetic field pattern.

Isn't it "produce an uniform magnetic field", or is the existing "produce a uniform magnetic field pattern" correct?

Answer

The word uniform begins with a palatal approximant /j/. The palatal approximant is a consonantal sound, even though the letter itself is a vowel. Since we use the pronunciation of the word following the article to determine whether we use "a" or "an", and because it is pronounced starting with a consonant, we use "a". Thus, the original sentence is correct.

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Just for the sake of completeness, the letter "u" can also have a vowel sound, such as in the word "umbrella", which begins with an open-mid back unrounded vowel /ʌ/.