em... so you've got your experimental data from XRD, ED, etc... (?) from some material which is orthorombic and you have your reference data for the same material. Probably there is some discrepancy from experimental data and from reference data, and you are interested in the error between them? And since you are mentioning the orthorombic system, probably the difference in both data set is only in certain directions?

I assume you've got preaks from XRD. First you find from which palnes are the reflections, that are "not right". Then you can compare the reflections with reference data and probably already you will have first idea in which directions your cell is contracted / expanded.

If this is not your issue, provide some more data about your problem.

Cheers!

Thank you very much@Janez Zavašnik for your response

You have to differentiate the equation for a, b and c in order to find out how big is the respective impact. 

Thank you sir @ Gert Nolze 

just a remark for other people reading this answer... if you have your lattice parameters, one can also use this free-software for comparing two structures of the same space group:

http://www.cryst.ehu.es/cryst/compstru.html

It will derive some "numbers" which can be usable...