Thanks for the that Fred. To be honest, I think this is getting a bit beyond my cut and paste coding ability. I'm thinking of downgrading this project to something along the lines of a digital pressure gauge, say three green LED's, three orange, three red, lighting up in turn as the pressure increases. Good shout on the deadband for the LED's, I hadn't thought of that. The hydraulic pressure is supplied by an electric motor controlled by a sexy Danfoss HVAC inverter rather than the diesel engine of the truck it came off, so its a very smooth power delivery. Reading off the analogue gauge the pressure spikes are very minimal, but I suppose a 0-4000 psi gauge isn't as sensitive as the Arduino. I'm really trying hard here to justify using the Arduino for something!!!