Digital desk display

Hi, I'm an electro tech virgin, so here goes -
I have a display on a control desk which is a duplicate of the main display on a control panel. The displays are used to show an earth leakage current, the panel meter reads 2.4 mA and the desk shows 0.7mA - the meters use a 0 to 10 volts signal. There is no adjustment on the desk display so what can I place across the terminals to tally up the two readings ? I hope someone can help - Thanks

An analog adder connected to an LCD will do it. A digital adder also works if it has a front-end ADC.