How close are the other stations, if they are not in your backyard then comparing rainfall with others isnt recommended
Get yourself a 4" manual gauge and mount it next to it and compare them over time, not just one storm, this is the advise
that i was given, the only downside to this is the 4" manual are more accurate than a tipper.
Was this over one storm or many? how is the gauge sited, i.s. is there anything above that could drip in to it?
Having said all that, 50% is quite a bit, have you looked at it the other way round, it could be the others that
are reading incorrectly?