I have the same panel
connected to the Xantrex controller repeating yesterdays solar charge of the engine batteries
(there is a constant parasitic drain which is why I rigged the make shift trickle start)
anyway the c40 works fine but the display module is damaged/wacky
the amps are always displayed as 1 amp even when the fluke, vellman, and craftsman say otherwise
at one point my digital meters said 2.46 amps & 14.3 volts 35+watts
the c40 display said 1 amp & 14.1 volts 14 watts
I tried unplugging the display and even pushing the reset button, but it still displays the wrong info
Oh well it was free, and the charge control apparently works
I have it for backup duty if ever needed

my test setup

meters, notice the difference between the C40 display readings (1 amp) and the numbers on the Fluke (2.07 amps) and craftsman (2.1 amps)
at one point the C40 readout did display 2.0 amps 29w 14.5v
but my fluke meter said 2.36 amps and the vellman meter 14.75v
which equal 35w going to the batteries
the Vellman digital is not in any of the pictures