From a carpenters perspective, I've set the angle with a couple of easy light weight options. You can't hike with a 4' (foot) level and a tape measure,     

   So option #1 is a string & a 2" string level. Rap the string around a rock, rap it around the top of the sluice. Hook the string level on the string. Now with the string around the top of your hand, go to the bottom of the sluice. If you have a  48" sluice then use your 4" wide hand as a measuring tape. So when the bottom of your hand touches the sluice's bottom and the string is level, you have a 4" drop. Adjust the sluice up or down, just keep the string level while using your hand or finger as a tape measure.

  Option #2 is the same thing but using a light weight 9" 'masons block' level & a string. It weighs nothing and it fits in a fold up sluice box.

    The old timers will say always have the water level at the middle of the sluice sides, & not over flowing & never so fast that it makes a rooster tail. Rooster tails just shoot the Gold right up into the end of the sluice box.

     Before high bankers made the seen we would set up our sluice boxes in the streams mostly by eye and the water speed in the box.  When we liked what we saw we would then throw in some small pieces of lead and a hand full of screened material.  If the lead stayed up top and the rocks walked not ran out of the box we figured we were good to go.

     Today I set my high banker at a 1 inch per foot drop using a torpedo level and a small tape measure.  Next the water speed is throttled to the rate that moves the material at a nice even walk out of the box.  Remember this gravity is our friend at a low slope and our foe at a high slope.

     Also just so you know 1 inch per foot drop on a protractor is 4 3/4 degrees.  At 10 to 12 degrees you are running over 2 inches drop per foot.          Ron

thanks ron, that's what I was looking for. I upped the water flow with pump size, that degree looked good with small pump but was ripping with the big one