cam belt change

[smudger 72]

Hi All,
Just bought an old V reg 1.9D Berlingo. Its beat up and seen a lot of miles but I love it.
At 129K I reckon I should change the cambelt. Has anyone done this on this vehicle?
Haynes say use an electronic SEEM testing gauge to get the right tension. But at over £200 I cannot justify thisillyme:. How did they guage the tension before these were invented:brickwall:? Can anyone advise me please?

[800HDI]

I've always used the twist through 90 degrees for every car or van i've done a cambelt on. Saying that though, when my van wanted doing it went to the garage.Too much work to do on the driveway!