Spot the deliberate mistake?!

[BeerSpark]

These are the terminals on a conductivity probe . This instrument has a function in the parameters whereby you can select a different measuring range via means of a binary input. It would appear that this has never worked. Not exactly sure what's entailed when commissioning a large project, but they obviously don't get in the field much!

Can you spot the error? Clue - something's missing!(Installed sometime in 2005!)

 

[ifindoubtdont]

At a guess I would say terminations in positions 86,81,82 and 94.

 

[Darkwood]

No negative return?

 

[nickblake]

as darkwood

 

[BeerSpark]

Yup! Not much of a circuit without it haha!