Thanks for explaining the weird characters, your post is very informative!!
Unfortunately (for me) I'm using Windows... don't get much choice with the Government!! ;D
I guess that's another option to look at; does anyone know of an existing Windows program which could convert the raw data to CSV or just plain text? I had hoped to have been able to just pull the SD card out, plug it into the laptop & view the output in 'real' numbers, but I now understand that I can't do that currently. I can't get over how generous the Arduino community is in terms of writing & sharing code with people like me, and I would be deeply grateful to have a look at a writeString() function if you were to play around with one!
Since my data is only taken once a minute, and the capacity of SD cards provides essentially unlimited storage in my case, speed and file size are not really an issue. Your comment:
In your case trying to figure out this string thing (its actually an array of chars) might be an idea.
...has got me thinking though, so I'll start playing around with that & see where it takes me...
Thanks again!