"He wasn't over by much but still miscalculated," his lawyer told the court.
Prosecutor Sergeant Garry Wilson said following the positive reading Guildford exercised his right to a blood test.
This resulted in a blood alcohol reading of 81mg of alcohol per 100 millilitres of blood.
The legal limit for an adult driver is 80mg.
Judge Morris said Guildford had a previous drink-driving conviction when he was found to be nearly double the legal limit.
She said it had been a "lack of fine judgement" by Guildford to drive this time as he was "just over the limit" but she warned him about the consequences of a third drink-driving conviction.
"Make sure you are not back before the court."
Judge Morris fined Guildford $600 and $130 court costs. He was disqualified from driving for six months and ordered not to have any interest in a vehicle during his disqualification period.