As you read on the page about [syllables](#/lesson/SpellingAndPronunciation.04), the combination _ch_ is treated as _one_ consonant.
Lachen --\> la - chen
As a consequence, _a_ is an open vowel, which we would classify as a [long vowel](#/lesson/SpellingAndPronunciation.09). But it is not!
Just remember, that every _single_ vowel (as opposed to double vowels and vowel combinations) that precedes _ch_ is a short vowel.
Had the Dutch not decided to treat ch as one consonant, the division would have been:
lac - hen. Here, the _a_ is safely enveloped by two consonants, and could thus be considered a short vowel.