That was what firefighter Kevin Smythe used to measure how far the rescue team could drill into the area where the former personnel officer was trapped in the Stockline Plastics factory rubble.
The 62-year-old from Erskine, Renfrewshire, was shown the footage of her rescue by Strathclyde Fire and Rescue as part of a TV programme, and she could not believe it was her.
"I felt I was maybe watching someone else being brought out," Ms Kinnon said. "They were saying: 'That's you, this is where you were.'
"Kevin Smythe said it was a 99p ruler out of B&Q that saved my life because he used that to measure how far you could drill."
Ms Kinnon still sends Christmas cards to the rescue crew at the Blue Watch in Alloa, central Scotland, who helped save her.
"I usually put in a wee update on what I've been up to that year," she said. "I send one personally to Kevin Smythe, but one to Blue Watch too.
"And I send one to all the wards at the hospital and all the doctors. To thank them.
"They put their own lives at risk."
A decade has passed since Ms Kinnon received her horrific injuries - her legs were crushed and a buttock was impaled with a roof truss.
She endured 10 weeks in hospital, another 13 in bed recovering and has had countless operations since.
Ms Kinnon now uses a walking stick to get around but needs a wheelchair for any distances.
She can still remember "falling down into a black hole" when the blast happened on May 11, 2004.
Ms Kinnon had been in her boss Stewart McColl's office preparing for a noon meeting when the explosion shook the building.
She said: "I can still hear the bang and Mr McColl saying: 'What the hell was that?'
"He went outside his office and I followed him."
She describes the feeling that followed as similar to when dentists use gas to remove a tooth.
"It was a sensation as if you were floating away," she said.
"Like you were falling down into a black hole. And I suppose I was."
Ms Kinnon fell 50ft and was trapped for nearly nine hours before being plucked out alive.
Mr McColl, who was trapped with her on top of her legs, sadly lost his life.
She said: "I thought I was conscious throughout but the rescue team have told me that I drifted in and out of consciousness.
"I did tell them a few times just to leave me alone because I'd had enough.
"I'd had enough with pain and the shock of it all."
Ms Kinnon believes training for a part-time job as a 999 operator may have saved her.
She recalls how she felt angry when Mr McColl died - because she was alone.
She said: "Mr McColl was moaning when I first came to. And I'd said to him all the emergency services would be out and not to worry.
"But I was a bit angry when he died. I was angry that I was then left alone in that hole.
"All I wanted was to make sure that everyone could get out.
"The only other thing I wanted was that somebody would look after my dogs. I think that kept me going."
Former dog breeder Ms Kinnon has still not come to terms with the disaster.
She still asks herself why she lived and others died.
She misses her mobility.
"I miss being able to wear a skirt," she said.
"There's scarring, holes in my leg where there wasn't enough flesh for the plastic surgeon to do anything with.
"I couldn't even wash my legs at first. My family did that. I couldn't touch them, it was horrific.
"And I put black bags on all the mirrors because I couldn't bear to see this creature struggling to get in and out of bed."
Despite the pain she is still going through, she is not angry over the "tragic accident".
Ms Kinnon, now divorced, lives at home with her two Yorkshire terriers Eilidh and Katie.
SHE says her family has helped her through the difficult 10 years.
Her nephew Charlie, 12, who is known to her as Chachi, and her niece Anna, three, give her hope and she spends time with them regularly.
Charlie, who was nearly three at the time of the blast, went to the site with Ms Kinnon's former husband when he had heard the news.
She said: "He just grabbed Charlie and came through to Maryhill.
"Chachi used to call me the bomb lady. He thought it looked like a bomb site.
"I've spoken to him about it since and he wanted to see the site again so I've taken him there."
It is her family who she will spend tomorrow with at her local church.
"Even if it was 20 or 30 years on the impact of it doesn't go away.
"I know there's a memorial service, but I will spend it at my own church with my nephew."