Make a number go to 6 decimal places and not round

You should use this AFNumber_Format:

if (event.value && !isNaN(Number(event.value))) {AFNumber_Format(6, 0, 0, 0, "", false);}

The Acrobat provided forms function call:

AFNumber_Format(nDec, sepStyle, negStyle, currStyle, strCurrency, bCurrencyPrepend)

nDec = number of decimals
sepStyle = separator style 0 = 1,234.56 / 1 = 1234.56 / 2 = 1.234,56 / 3 = 1234,56 /
negStyle = 0 black minus / 1 red minus / 2 parens black / 3 parens red /
currStyle = reserved
strCurrency = string of currency to display
bCurrencyPrepend = true = pre pend / false = post pend

Yes, use this:

var num = event.value;
var dec = num.match(/^-?\d+(?:\.\d{0,6})?/)[0];
event.value = dec;