The test we use for static thrust -goes like this.
The helper stands over the rear of the plane - -holding the force along the root of the stabs.- wuth his legs.
A line is hooked to the rear of the model -and to the scale .
pick a solid location.
I hold the scale aligned with the attached line.
Then the engine is advanced to full throttle -and I pull on the scale , till the model is backed slightly away from the holders' legs.
A few trials will tell you if the setup is aligned, as the readings will all repeat.
This also insures that the plane does not scoot away -if the line or scale fails.
Don't be surprised if the actual thrust is nothing like the friggen chart suggests.