One of the concerns from the WCO's viewpoint is that testing and verifying the acceptability of electronic weight and balance programs is very involved if one is to be able to say, definitively, that the program will not give an incorrect answer. From a practical point of view, the testing would be commercially prohibitive for most operators to achieve a WCO's signature. Many years ago, I dabbled in software development for industry operators and, I have to say, I was horrified at just how innovative the end user could be when it came to finding flaws in program logic.
So how can we get around the problem ?
My view is that I will approve a suitable paper based system and am quite happy to include a rider that the operator may implement the approved paper system in a suitable electronic program providing that adequate software testing is performed by the operator to ensure accurate output. The approved paper system, though, remains the definitive approved Loading System. I note that a colleague adopted a slightly different approach for the operator of a 100-seat class jet .. there was a very extensive in-service test period using both systems. I guess that has some merit but remains an expensive exercise.
FWIW, I am amongst the most experienced handful of WCOs in Australia, and hold the first WCA issued back in mid 1976.
Why would CASA be concerned about how I do my calculations?
So long as you can demonstrate that your computer-generated outcome is functionally identical to the approved paper system, I doubt that CASA would have any real concerns. The secret, here, is to make sure that your electronic system replicates the approved paper system without trying to do too much in the way of additional fancy stuff. After all, the aim is to ensure that the aircraft remains within the approved envelope at all stages of flight .. no more, no less. If you want to do fancy stuff, do that separately and then link back to a basic mirroring program to tick the box for weight and balance as being OK.
This is particularly the case if your aircraft/operation doesn't require a load sheet per CAO 20.16.1.
If your question relates to having the WCO approve someone else's compiled electronic system other than one which mirrors his .. along with a whole bunch of bells and whistles, then all bets are off.