I deliberately made sure that I noted the weights on my scales and those at both ends of my trip. I remain convinced that this is one area that thy are ripping people off
Agincourt / cmorris04 - this kind of thing happens from time to time at airline checkin desks - American Airlines landed themselves in hot water for having incorrect scales at checkin desks - I believe the FAA decided to get involved and American quickly implemented new procedures to avoid reoccurrence of the problem.
While there will always be the very occasional mistake (no machine is completely immune from being faulty), it is certainly possible that some airlines get their scales wrong more often than others.
If you suspect this is the case, I would *strongly* recommend you contact your local trading standards office. While they are often reluctant to get involved with minor cases involving a single person, the UK Weights and Measures Act means that if they have grounds to believe a business is flouting the law and failing to test their weighing equipment properly on a regular basis, they will act.
The next time this happens at an airport to which other airlines fly, if you have the time available, you might perhaps like to ask at a checkin desk from another handling agent / airline to validate the weight. Weighing things yourself also can play its part. Even better, if you can get the record of your independent weighing on camera / video on your mobile phone, this will give trading standards greater incentive to act.
If the issues are occurring at airports outside the UK, you might like to ask trading standards for details of the similiar legislation in the respective country, and send an email to the relevant Govt body. I've made complaints about this in the past in the UK to trading standards (a major reputable UK supermarket in a branch were selling 250 gram packets of grapes labelled as 500 gram and the store manager didn't want to know - probably just an accidental labelling screwup at a warehouse), and they have been acted upon.