ISO settings

Hi me again.! Camera is A620 Says in Advanced Guide that when camera is set to Auto it automatically sets the sensivity to produce the optimal image quality. Default is ISO 50. When shooting in Auto mode should I leave the ISO at default 50 or change it to Auto.? Its very cloudy outside today notice that at ISO 50 I get a very slow shooting speed ./60 , but if I change to Auto ( on the ISO line) then I can get a bit more /80 or /100. This is just comparing in the LCD when I press the shutter button 1/2 way down..
So shooting in Auto or P which should I set it at ? I do not to use manual.
Have been leaving at it Default up to now & the pics seem o.k when printed 6x4.
Thanks. Storm

If you've set the camera (not the ISO) to "Auto", the camera uses Auto ISO no matter what you may have set. You can't set an ISO in Auto. When they say "optimal image quality" they mean it will adjust the ISO up or down to give you a better (hand-holdable) shutter speed. If you don't want to fiddle with things, I'd say use "Auto" ISO unless it's very bright out; then reset it to ISO 50.