88, I think your math is correct, just not applied as a photographic term. If you lost 100% of your bodyweight, you would indeed be gone.
In a 100% crop you are looking at the photo pixel to pixel on your screen(as someone else stated 1:1). It's not much good for much except for pixel peeping to determine quality of one thing vs. another. At that crop since you are viewing pixel to pixel you are seeing minimal distortion since you are getting no compression or interpolation by the computer. At 100%, here is what you are doing. To make it simple, if your screen is 1500X1000 pixels, and your photo is raw and native resolution is 4500x3000, at 100% you will be looking at 1500x1000 pixels of your photo which is exactly the same resolution of your screen. If you scroll it accross your screen you will get 3 even scrolls across your screen(1500 pixels per 3 scrolls=4500). If the native raw resolution of your camera is only 1500x1000(1.5megapixels), at 100% you will be able to fit the entire picture onto your screen at 100% at one time or 1:1. The more pixels the photo or the lower pixels your screen the less of the foto you will be seeing at 100%. For pixel peeping you want to look at it in raw with no PP at all. Once it has PP or converted to jpeg you have altered the file and either introduced compression or interpolation. It would still be a 100% crop but has lost its value for comparrisons except to itself.
As for cropping a foto, aspect ratio and ppi is completely different. I always convert to jpeg in inches instesd on ppi, that way my final print will fit my paper at whatever dpi I choose. If you want it to fit onto your paper exactly w/o the printer cropping it for you then before you convert you will have to crop it to the same aspect ratio as your paper before converting. Don't confuse input(ppi) with output(dpi).

Dam! Have I just wasted my money on an IR filter I can't use....I did this recommended test with my 20D and my viewfinder was black! Any advice please?? Darryl

Hi Steve, Thanks very much for all the info you have given me/us. I am using a Canon 20D and unfortunately I don't have 'live view' (I am very glad I have kept my Canon S3 IS with it's articulating LCD). I can see nothing through my viewfinder. I have just taken some test shots and these are my settings......Bright sunny day, 18~55mm kit lens, ISO 200, f8. I set f8 just in case I moved my focus slightly while putting the filter on. I set the focus using auto (no IR filter) and then switched to manual focus and put the filter on. I took a series of shots at 2 sec intervals starting at 2 sec thru to 10 sec. I then went 15, 20, 25 seconds. All the pictures turned out exactly the same....total 100% black.....Blast ~ I have just remembered I left my WB on auto - I will go and take more shots (I see you did recommend setting the WB with either white paper or the grass). Darryl

I've been looking around for some more info on the R850, but as usual its not very forthcoming. One quick question, with the filter on the camera, can you see anything in the LCD viewer.

With the RM72, you can actually see enough to compose, and also use your auto focus. Although it looks all red, still you can see. This is the small amount of visible light, or near IR the RM72 passes being seen.

Of course you have to be using a fairly small F stop, like F4 or less. And a slow shutter setting. My camera for those shots was set at; Manual Exposure, ISO 100, F4, shutter 1.6 seconds. And I had a fairly good image, on the LCD.

Of course how much you can see, will all depend on how IR sensitive your camera is in the first place.

Ok, first your camera must accept filters. Second you need to do an IR test, to see if the camera is compatible.

Set your camera on something like F2.8, or whaterer your widest aperture is. Point a Tv remote at the lens, no more than a foot away. Look in the LCD display if you see the IR light, and it is pretty bright your camera is a good candidate. If it is dim, you can still take IR images but with very long exposures. If you can't see it at all, don't even waste your time or money.

If everything checks out OK, you need an IR filter like a Hoya R72 sometimes called a RM72. Mine was $89.95 from B&H. If you went this far inquire back for other particulars, for after you take the shot.