Gauge graphic ? first time

Hi to all,

First time i’m actually doing a GAUGE graphic and i need to create many of them but i don’t really know where to start and maybe some quick start on an example would help me.

I need to display a gauge in order to compare between thess 2 metrics: [Units this year] and [Units last year]

Can someone please let me know the basic lines on how these 2 metrics can be displayed on the GAUGE ?
What goes in the Default measure ? ==> Is it the standard TOTAL UNITS metric
What goes in the Series ? ==> Is it my 2 metrics i want to compare ? Or simply one of them ?
What goes in the Categories ? ==> Is it the other metric ?
What about the Default Axis ?

Thanks in advance for any valuable feed-back !