Three flashes are metered, Yongnuo YN-565EX, Neewer VK750 II, and also the Nikon SB-800 for reference. The idea is about comparing their actual power, and to show what their expected aperture results might be, in an umbrella and also direct flash (notice the shadows). Each flash is metered with a handheld incident meter, and this value is used for an actual picture to be able to judge and verify it.

All of the pictures should be equally exposed, because all were metered individually to make that be true. The actual camera f/stop metered and used for each is shown in a picture for comparison.

All pictures below are ISO 100, with Nikon D800, 1/125 second shutter. Flashes are always 1/1 Full manual power level, and zoomed to 24 mm. Each flash is placed on the same light stand.
Each flash is metered from above the brown bear's ear, to ensure from exactly the same location (incident reading with Sekonic L-308S meter).
White Balance is individually corrected on all, using the Porta Brace White Balance card in Photoshop CS6 Adobe Camera Raw. Correction leaves the card being a neutral color with equal RGB components (no color cast).

Metered in tenth stops, which are just that... A third stop is + 0.33 stop, and 2/3 stop is + 0.67 stop.
f/5.6 + 0.9 stop is almost f/8.   f/5.6 + 0.6 stop is f/7.1 (2/3 stop past f/5.6), etc.
The necessary nearest third stop camera aperture setting might be up to 0.17 stops different than the true metered value.
FWIW, the purpose of tenth stops is for adjusting multiple lights. If we want fill ratio to be 1.2 stops less than main, we immediately know in our head that 1.2 stops less than f/5.6 + 0.9 stops is f/4 + 0.7 stops. Try computing that from f/7.1. 😊