Just to add I've put all the different stages into studio, I've only been using it a couple of weeks and don't know how i managed before,

I'm still not sure why SUMMARIZE, can see a single column table returned, as opposed to the entire table

I know this doesn't work but can't see why; 

 MINX(
                                                       TOPN(3,Table1,Table1[Units]), Table1[Units]) ,
                                                                Table1[Units])
can't work,

Richard.