I've looked at your app on a 7" tablet (800x480) and a 10.1" tablet (1280x800). I see that you have a couple of dozen layouts, one for each type of calculation with a portrait and landscape variant for each, which brings you up to about 50 layouts.
You said: "on my 7" tablet everything displayed as it should." What is the resolution of your 7" tablet? Your layouts are done at 480x320x160. If your tablet is the common 800x480x160, then your layout should take less than half the screen, which is how it appears on my 7" tablet of 800x480x160.
On my 10" tablet, it only covers about an 8th of the screen. This makes the text, EditBoxes and Buttons correspondingly tiny.
As noted under Common Device Sizes in the Wiki under
Layout Variants:
Notice that both the Xoom, at 10.1" [1280x800], and the Archos A70, at 7" [800x480], have a scale of 1. This means that Android will not change the size of the views despite the increase in number of pixels, which means that the same layout on the Xoom will look much smaller than on the A70. (See the screen shots in the
Introduction, above.) One way to adjust for this is to do a separate layout for 1280x800x160 devices in which you manually enlarge all the views, the text sizes, etc.
This means having a different layout for each of your current (couple of dozen) layouts, each with two variants, which will result in about 150 total layouts. (Ouch!)
Also note that to solve the size problem, you must do new layouts for the different sizes apart from the original layout files. If you did new variants inside the existing layouts, changing the text sizes on one size variant would also change the text size on the other variants, which you don't want.
Another (much smaller) problem is that when I get past the splash screen and "evaluation version" notice box to the input boxes and start entering data then rotate the screen (perhaps accidentally), I lose the data I've entered and have to go through the splash screen and "evalutation" notice again. To avoid this, see
Saving An App's State in the Wiki and the following section on using Activity_Create, Pause, and Resume.