The first type occurs in a stressed syllable before a fortis consonant, so that e.g. bet [ˈbɛt] has a vowel that is shorter than the one in bed [ˈbɛˑd].
Vowels preceding voiceless consonants that begin a next syllable (as in keychain /ˈkiː.tʃeɪn/) are not affected by this rule.
Because of the variability of vowel length, the ⟨ː⟩ diacritic is sometimes omitted in IPA transcriptions of English and so words such as dawn or lead are transcribed as /dɔn/ and /lid/, instead of the more usual /dɔːn/ and /liːd/.
Compare the length of the RP vowel /ɒ/ in the word not as opposed to the corresponding /ɒ/ in Canadian English, which is typically longer (like RP /ɑː/) because Canadian /ɒ/ is a free vowel (checked /ɒ/ is very rare in North America,[citation needed] as it relies on a three-way distinction between LOT, THOUGHT and PALM) and so can also be transcribed as /ɒː/.
Many speakers of Serbo-Croatian from Croatia and Serbia pronounce historical unstressed long vowels as short, with some exceptions (such as genitive plural endings).