A little explanation is needed. When dinosaurs ruled the earth, Cathode Ray Tubes used Electron Guns to excite a phosphor layer on the inside of the CRT.

Sony Trinitron

Trinitron - Still a Mystery? 

2.5.2.4.7 Focus and Convergence 

Select mode 4 (or mode 3 if not available) to display test patterns.

1.  Select option 1, pattern A (Crosshatch),

2.  Adjust focus control on video shield to focus vertical lines.

3.  Adjust focus control on EHT transformer to focus the horizontal lines.

4.  Press PF3 to return to setup patterns.  Option 5, pattern E (Focus Pattern), check focus settings.

5.  Press PF3 to return to setup patterns.  Option 1, pattern A (Crosshatch), and press  spacebar to get a white crosshatch pattern.

6.  Adjust H.STAT control on video shield to set convergence.

  This completes the alignment procedures.