I just bought a used lesco spreader with 80 lb hopper. I think it is just a year old. The old owner just used it for salting ice and no longer needed it so i got it cheap. So I bought a bag of lesco fert, 24-2-11, and it says to use the calibration gauge #15. The spreader has 2 plastic "gauge feelers" and also has the dial settings. I think there is a number 15 setting on the dial, but is that different than the "calibration gauge #15"? Thanks for your help. PS. I only fert my own lawn, so dont flame me.