<?php

$precision = 18;

while($precision--) {
  ini_set('precision', $precision);
  echo $precision.":".(342349.23 - 341765.07)."\n";
}

17:584.15999999997439
16:584.1599999999744
15:584.159999999974
14:584.15999999997
13:584.16
12:584.16
11:584.16
10:584.16
9:584.16
8:584.16
7:584.16
6:584.16
5:584.16
4:584.2
3:584
2:580
1:600
0:600