Turn on the Midas DL431 using the power switch(s) on the rear panel. For determining the Software Version you can switch on just one. Once the unit has fully booted, press and hold in the 'Menu' button. The software will then drop into a numbered Menu. Using the Up or Down arrows, scroll round to option 6 - S/W Version. Press the 'Enter' button and the software version the unit is running will be displayed. Pressing the 'Menu' button twice will drop you back to the normal operating page.