I recently took photos on a hiking trip using a lot of fill-flash, some with an external flash and other with the built-in flash. It was clear from the result that the built-in flash didn't have enough power to lift shades on that particular bright day, even with the flash compensation at +2 ev. With my Nissin 466 flash, I obtained satisfactory results at 1/4 power under the same circumstances. So, what is the guide number of GH1's built-in flash? I'd like to have a better sense of its power, so I can quickly decide whether to use the built-in flash, or get the external flash out instead.