Relative presision removes the need to specify a precision (so it's easier to use), but it has limits.

For example, most numbers in the real-time control system on which I work are have a range of 0 to 1 (inclusive). Some of the numbers with which I deal are measurements of valve positions. 0 means the valve is fully closed, 0.25 means it's one quarter open, and 1 means it's fully open. If we were to compare two valve positions, we'd consider 4/1000th open and 5/1000th open equal. Because relative precision has no idea these measurements are tiny compared to the range, it would consider them unequal.

In my experience (in the real-time control systems world), relative presision should only be avoided whenever possible. Absolute precision should be used instead.

Update:

Oddly enough, we rarely use any kind of tolerance in our system except during automated testing. Equality checks are rarely if ever needed. Inequalities, on the other hand, are used throughout. We use deadbands to avoid jitter. 

if ($x < 0.5) {
   # All is ok
   $ok = 1;
   ... normal operation mode ...
}
elsif ($x > 0.7) {
   # Things are definitely bad.
   $ok = 0;
   ... exceptional operation mode ...
}
elsif ($ok) {
   # In deadband. Was last ok.
   ... normal operation mode ...
}
else {
   # In deadband. Was last bad.
   ... exceptional operation mode ...
}

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In reply to Re^4: Infinite loop but no reason why by ikegami
in thread Infinite loop but no reason why by Anonymous Monk

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