Am I conducting photometry correctly in the APT program?

Hello. Are there people here who know how to work with the APT (Aperture Photometry Tool) program? I just would like to find out if I am doing photometry correctly in the program. I open the image (not calibrated), click on the comparison star to see the value in the field: Source intensity (the sky is tightened). After that I go to AAVSO to find out the exact shine of the star in the B filter. I calculate this and the intensity value of the source using the formula to calculate the zero point of the amplitude: a + 2.5 * LOG (b) (where a is the value of the star in B, b is the intensity of the source (the sky is tightened)). Then I write the result in the field: Zero point of magnitude. I am conducting photometry (in the program I installed: Model 0 = Interpolation of the radial profile without an aperture and model B = subtraction of the median of the celestial ring). I click on the comparison star and see that the value does not match the AAVSO (VSP) card. I am starting to increase or decrease the circles on the viewport so that the value of the comparison star matches the value on the VSP map. When the magnitude matches, I begin to conduct photometry of the comparison star, after which I record the data and send them. Am I doing everything right?