http://en.wikipedia.org/wiki/Finite_difference

http://en.wikipedia.org/wiki/Numerical_differentiation

http://mathworld.wolfram.com/DifferenceOperator.html

http://www.arpnjournals.com/jeas/research_papers/rp_2010/jeas_0710_364.pdf

http://math.fullerton.edu/mathews/n2003/richardsonextrapmod.html

http://turing.une.edu.au/~amth247/Lectures_2003/Lecture_18/lecture/

http://www.math.siu.edu/matlab/tutorial5.pdf

http://dmpeli.math.mcmaster.ca/Matlab/math1J03/LectureNotes/Lecture4_1.htm

http://arxiv.org/ftp/arxiv/papers/0809/0809.0465.pdf

http://www.gaf.ni.ac.rs/cdp/FIN-DIF-INTER.pdf

ftp://ftp.demec.ufpr.br/CFD/bibliografia/MER/Burg_Erwin_2008.pdf

http://pages.intnet.mu/cueboy/education/notes/numerical/newtongregory.pdf

http://mathworld.wolfram.com/FiniteDifference.html

http://ocw.mit.edu/courses/mechanical-engineering/2-29-numerical-fluid-mechanics-fall-2011/lecture-notes/MIT2_29F11_lect_14.pdf

http://www.encyclopediaofmath.org/index.php/Richardson_extrapolation

http://www.math.odu.edu/~jhh/chs4.pdf

http://www.lce.hut.fi/teaching/S-114.1100/lect_3.pdf

http://www.math.wsu.edu/faculty/genz/448/lessons/l501.pdf

http://www.csun.edu/~lcaretto/me309/pa5Soln.pdf

http://www.phy.ohiou.edu/~elster/phys5071/extras/Morton_Ch6.pdf

http://reference.wolfram.com/mathematica/tutorial/ApproximateFunctionsAndInterpolation.html

http://persson.berkeley.edu/128A/ch3.pdf

http://persson.berkeley.edu/128A/ch4.pdf