Hi synthetic,
I did not test out empirically, but here is what the manual says:
"Main mode switch"(= left upper switch): => "Full": Strobe always makes full dump
=> "M": Manual flash mode other than FULL amount (positions from "-0.5" to "-6").
In "M" mode the right upper switch can be turned from -0.5 to -6 EVs. So it is actually 71% (2^-0.5) to 1.6% (2^-6) of full power - in case the flash does really what these numbers imply...
The two big switches are o.k. to operate, but the two small ones sometimes change position unintentionally, when I change the settings on one of the two big switches (at least with gloves): a tool to block both small buttons (focus light to "off" and preflash cancellation to "off") would be perfect for my needs...
Wolfgang