Using an incidence meter such as the Robart is pretty straightforward. Just secure the airplane in a level configuration (using the built in level and gauge) you then simply slide the meter's calipers together over the leading and trailing edges of the wing or stabilizer and note the indication on the needle. Generally when setting up a biplane, start on the lower wing, and then do the top. The robart meter costs about 38.00, which is cheap insurance against awkward snap/stall situations, and generally poor performance due to poorly set up decalage. It is pretty tough too. . so you will have it for a long time!

Best of luck,
Brett