Hi MP, This is just what I was looking for, thanks a million. Just one (or two) question for now as I set about making it: Q: Do you think that they have got the resistors, R1 through R5 in the wrong order? It looks like R5 should take the place of R2 and R2 through R4 should all move down one. Q: What values would you recommend, for the sensor resistors, if use 10 sensors instead of the five as in this schematic as my tank is 5 metres deep? Best regards and thanks again, Bob…