which needle is which

I finally am putting my cluster back together. I finally got my white face red letter gauge face. I used Mcguiers clear plastic polish and cleaner on the clear plastic lens that covers it. Works awesome!! Took out all the scratches. Those lens scratch real easy and the one I bought was in tough shape. It's as good as new now.
The housing that covers the gauges. The flat black part that has fuel written on one side and temp written on the other and goes on top of the gauges. Has anyone changed the color of this? It's almost too black now.
My other question is I noted the needles are a little different one has a piece of metal sealed to the bottom of the fat part of the needle. The other one doesn't. Which one is for the tach and which one for the speedo.
And while I think about it what's that little lever for on the speedo side that moves that spring?