Hi Tom,

What ranges are we talking about? Are you interested in altitudes higher than 21501 feet? If not, you can treat your input as a word(skip top 8 bits) and do your calculations on that. If you need to go higher, things will get more complicated but still possible. Higher than 65535 feet will get nasty ....

Do you really need 0.1m(0.3feet) resolution? Will 1m(3feet) enough?

Another thing .... you need to know how your inputdata(24bits) is formatted. My guess(based on your information) is that you are located at about 1096 feet. I'm assuming that "alt[3]" contains the most significant byte, 0,13,13 would be 000D0D in hex which is 3341 in decimal. 3341 tenths of a metre is 334.1m which is 334.1*3.28084=1096 feet.

/Ingvar