How can I check the divergence?

• Always wear laser eye protection during this test.
• Project the beam onto a matte black surface at 1m from the aperture of the laser  A metal surface painted with flat black paint works well.
• Measure the diameter of the beam in mm excluding the area where the brightness is less than 20%.
• Measure the beam diameter again at 11m from the aperture of the laser, excluding the area where laser power is less than 20% of the beam center.
• Subtract the value measured at 1m from the value measured at 11m.  Divide the result by 10.  This is approximately the divergence in mRad (milliradians).