It may have cost Rosemary Gamble up to $2,000 to have an engineer check her jumping castle and ensure it was being safely operated, a court has been told.

Roderick McDonald, an inflatables expert and mechanical engineer, continued giving evidence in the criminal hearing of Ms Gamble in the Devonport Magistrates Court on Tuesday.

He said Ms Gamble was not a competent operator of a jumping castle.

Ms Gamble has pleaded not guilty to failing in her workplace health and safety duty over the Hillcrest primary school tragedy on December 16, 2021.

On that day, Zane Mellor, Peter Dodt, Jalailah Jayne-Maree Jones, Addison Stewart, Jye Sheehan, and Chace Harrison died, and three of their classmates were seriously injured, when a "mini tornado" tossed the jumping castle across the school oval.

Ms Gamble's business Taz-Zorb was operating the jumping castle and zorb balls, and is accused of failing to properly anchor the jumping castle to the ground or mitigate risk factors.

Defence lawyer Chris Dockray argued in response there was nothing Ms Gamble could have done on the day to prevent the tragedy that unfolded.

Engineer not engaged, court hears

Mr McDonald told the court on Monday that to ensure safety, operators of devices like jumping castles should be either following manufacturer's instructions "to the letter" or engaging an engineer to develop a safe operating procedure.

Robert Monte, Ms Gamble's partner who also helped with Taz-Zorb, said she had never engaged an engineer.

Mr McDonald said a national association of engineers that he chaired had about 26,000 members who would be able to complete such an inspection.

At this point, a victim's family member in the rear of the court nodded her head while appearing exasperated, and looked around at other family members.

Mr McDonald said if one engineer was able to complete such an inspection in two days, it would cost a business owner between $1,000 and $2,000.

The court has previously heard the jumping castle itself was purchased in 2015 for about $3,500 from Chinese manufacturer East Inflatables.

Mr McDonald said Taz-Zorb was inconsistent in their operation of the jumping castle, and that Ms Gamble was not competent to make the necessary safety assessments or deviations from the manufacturer's instructions.

On several occasions Mr McDonald described Taz-Zorb's approach as inconsistent, and again on Tuesday morning, compared the need for consistency in jumping castle operation to road safety.

He also told the court that although the jumping castle was not being operated competently and the anchors used did not meet Australian standards, Taz-Zorb's issues all could have been "remediated or managed".

It is expected Mr McDonald's evidence, including cross examination by Mr Dockray, will continue throughout Tuesday.

The court has heard the hearing before Magistrate Robert Webster may end this week.