thanks Tele/ Ken, so it's not at 60 or even 125 for strobe, at oddball 100? And for chrome if I nail it perfectly on light meter at that, open up 1/2 stop should be good?
With flash, shutter controls ambient light exposure and aperture controls flash exposure. If the camera only shoots f8, you will need to meter the flash power to f8. If you are trying to balance it to ambient light in a room or outdoors, that gets a lot trickier because there is virtually no exposure control on the Holga. And, Sunny 16 for ISO 100 film would be 1/100s, f16, and ISO 100. To get the reciprocal for f8 you would add two stops of light, so 1/100s, f8, ISO 100. BUT, the camera can't do 1/100s so I suggest ISO 50 film such as CineStill, or adding a 1-stop ND filter, or decreasing strobe output by one more stop. You can't vary shutter speed, you can't vary aperture, and if you're absouletly stuck on ISO 100 that's only going to leave one variable to control exposure--flash output.
There is one other technique to try--open flash. This is how it was done before the 1930s. I took a studio flash shot of a woman using my 4x5 and a lens made in 1858. Not only was there no flash sync back then (LOL!) the lens has no shutter. So, how did I do it? I set up my White Lightning X3200 in a huge soft box, radio trigger. Held the radio transmitter in my hand. Focused the camera, loaded the glass plate. Turned the room light down very low. Put a black t-shirt over the lens, removed dark slide (t-shirt blocked light from hitting the negative.) Quickly pulled the t-shirt away from the lens, popped the flash, immediately recovered the lens with black t-shirt. Replaced dark slide. Photo was a success! Below. It was simple because the flash was the only light I needed to account for.
So, Holga on a tripod, put in "bulb" mode. Meter flash so it looks good at f8,ISO 100 maybe 1 second shutter speed. Darken the room. Open the shutter on the Holga, immediately pop the flash, immediately release the Holga shutter. Done. Using chrome film is going to make this far more difficult but if you have the money for all the processing and expensive film, you will eventually come close. Not sure I'd use the phrase "nail it" with Holga shooting E6, but theoretically possible.
Kent in SD