I use pieces of 2x4 and scrap balsa under the fuselage to get the fuselage level front to back and side to side (as it should look when the plane is flying). Do not use the landing gear as the LG may be off slightly - you need to block the fuselage itself. The"eyeball" method is NORMALLY close enough for our needs. Then put your incidence meter on the main wing and continue to add/remove shims as needed until the main wing reads 0 incidence (or whatever incidence is called for). The main wing and the horizontal stab must have the correct angles of incidence for the plane to fly properly, even if the fuselage is not level front to rear (rare ).

Now, with everything still blocked up, put "T" pins through the horizontal stab and pin the stab in place, or in the case of most ARFS, slide the horizontal stab into the opening. Now with the main wing at 0 degrees (or what ever is called for), put a small level on the horizontal stab. The small level should be at 0 degrees in all instances.

If the stab is not at 0 degrees, you will need to sand/shim until it is at 0 degrees. While you are doing this also make sure the horizontal stab is parallel to the main wing. Sight from the tail of the plane forward. The amount of daylight showing under each tip of the horizontal stab and the main wing should be the same. You will also need a piece of string to make sure the distance from each tip of the horizontal stab to the tip of the main wing is the same length.

One everything is ok, remove the pins, or slide the horizontal stab out, and epoxy the horizontal stab in place. Recheck the distance to the main wing tips with the string and adjust as needed.

Let dry.