Once VTad has found the appropriate file for the rule key, the rule itself can be interpreted. Each rule is another hash, containing directives for threshhold comparison. Use this trick when you need to compare to a different key, or when you need to compare to the 0th key. Another compare trick is that negative numbers are interpreted as positive constant values. The amber threshhold would be 2048 kB. Finally, compare may be set to a user-definable subroutine.
More complex subroutines can perform arbitrary tasks.
The user subroutine is passed the current value, whatever that is, as a list reference. It is up to the user code to process that data, or to ignore it and do something else entirely. The user subroutine is expected to return a single number for comparison with the red and amber threshholds. The remedy is only displayed when the red threshhold has been crossed. Added dynamic history depth.