Complex sentence: Magnitudes are expressed within the table are when the stars are either at maximum brightness, which is repeated for every cycle, e.g., the eclipsing binary Algol; or, if the variations are small, as a simple average magnitude.
Split into simpler sentences: Magnitudes are expressed within the table are when the stars are either at maximum brightness, which is repeated for every cycle. I.e. The eclipsing binary Algol, or if the variations are small, as a simple average magnitude.