This setting does three things:

1.It tells the instrument to STOP RUNNING THE TEST because it could not pressurize the package to within + or - this percentage of the programmed pressure. 

Example:  If you have set a 10% TOLERANCE and you are running a LEAK TEST at a PRESSURE setting of 5 psi and during the CHARGE cycle the package only reaches 4 psi the instrument will stop putting pressure in the package and display ERROR.  

From the operator’s manual:

    The ERROR result for a Leak test means that the package could not be pressurized to the lower limit of the test pressure range during the Charge Time.

This may indicate a package problem or incorrectly set test  parameters such as too short a prefill time or too hight a test pressure specification range.

2. It also tells the instrument that if during the SETTLE cycle the pressure inside the package has lowered greater than the % TOLERANCE that there is a GROSS LEAK and will stop the test.

(The SETTLE cycle is where the instrument has reached the PRESSURE set point and is within the     % TOLERANCE so it now pauses, giving the package time to stretch r expand)

From the operator’s manual:  

The Gross Leak status for a Leak test means that the lower limit of the test pressure range could not be maintained in the package during the Settle Time.

Example:  If you have set a 10% TOLERANCE and you are running a LEAK TEST at a pressure of 5 psi and during the SETTLE cycle the pressure drops to 4.2 psi the instrument will stop the test and display GROSS LEAK since the pressure change is 0.8 psi which is 16% of the 5.0 psi set point.

3. For a burst test this setting tells the instrument that the package has burst in the event that it sees a pressure loss of this percentage or greater. 

Example:  If you have set a 10% TOLERANCE and you are running a BURST TEST, as the pressure continues to rise but let us say suddenly, the package stretches greatly but has not burst and the pressure drops slightly but not greater than 10%, the instrument will continue to put pressure in the package until it bursts and the pressure drop is greater than the 10%   

What to do:

In either situation to correct the issue and to be sure that there is not a gross leak try setting the TOLERANCE % to 30% or more.

Also, you might see the ERROR message because your CHARGE TIME is too short so also try increasing this in order to give the instrument enough time to get to full pressure in the package.  

By changing the % TOLERANCE you are NOT changing or effecting the accuracy of the instrument or the test.  The instrument accuracy is its only governed by its ability to detect extremely small pressure changes.