Sanal. aal763 is right. I too have had problems guessing myself to setting the altimeter correctly. Use the mouse, if you have difficulty zoom into the panel. There is also a good explanation in the FAQ section:

Q: How can I set the altimeter without being able to read the setting?

A: If you put your mouse cursor on the altimeter gauge, a little ToolTip message will come up showing you your current setting in millibars and inches, start then scrolling with your mouse wheel or left button and you will be able to set it to standard alt-setting by keeping on reading the readout from the little pop-up window.
Also check out the FSUIPC settings. Assign a hot key setting for required numbers through this program. Now you don't have to see the settings to know they are correct. Use "B" to give you the current alt setting and "Ctrl+B" to get required numbers.



Good flyings!