Two Nelson bars have had their $750 fines withdrawn by the Nelson City Council after it was discovered that certification for equipment used to determine decibel levels was out of date.

Environmental Inspections Ltd environmental officer Stephen Lawrence has taken responsibility for what he called a ``simple oversight'', after failing to ensure the sound level meter used to record noise levels had a current calibration warrant.

``It was an oversight, but as soon as we realised, we got the problem fixed immediately. There was no suggestion that the meter was reading incorrectly - it was simply that the sticker was out of date,'' Mr Lawrence said.

Environmental Inspections provides noise control services on behalf of the council.

The oversight was brought to light by a patron at Molly's Bar last week, who asked to see the reading equipment being used by an officer, and discovered that the calibration certification had expired last September.

The patron, who declined to be named, has an electrical background and used to calibrate the type of meter being used by the officer.

``He did his reading and I asked him if I could have a look. He rolled the meter over, and on the back the calibration certificate gave an expiry date of September 2007,'' the patron said.

Mr Lawrence said Molly's Bar had earlier been served a noise abatement notice over noise levels, leading to last week's fine, which had since been cancelled.

Molly's Bar declined to comment.

The other bar fined since last September had now been refunded the $750, Mr Lawrence said.

``There is no suggestion this will affect the integrity of readings done in the last two years.''

Environmental Inspections manager Bob Askew said the council used two types of noise level recording equipment - a sound survey meter and an integrated sound level meter that had to comply with New Zealand standards. The calibration of the sound level meter was checked and certified every two years.

Mr Lawrence said that in the past two years, 12 abatement notices or warnings had been served on licensed premises in central Nelson and on the city fringes.

Six infringement fines had resulted, including the two handed out since September, which had now been cancelled.

Mr Askew confirmed that the meter was reading correctly, but the calibration sticker was out of date.

He said more stringent measuring of bar noise stemmed from a recent Environment Court case, which ruled that the council had to take noise readings from outside offending businesses, not from the property of the person lodging the complaint.

Bar owners have since been working with the council to ensure their premises do not exceed the 55-decibel limit in town after 10pm.

Mr Askew said increasing concern about inner-city noise was an emerging issue as more people moved into the central city to live.