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

http://www.facstaff.bucknell.edu/mastascu/econtrolhtml/freq/nyquist4.html

http://www.facstaff.bucknell.edu/mastascu/econtrolhtml/freq/nyquist2.html

http://lpsa.swarthmore.edu/Nyquist/NyquistStability.html

http://www.personal.reading.ac.uk/~sis01xh/teaching/CY2A9/Lecture8.pdf

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=7&cad=rja&uact=8&ved=0CE8QFjAG&url=https%3A%2F%2Fwww.calvin.edu%2F~pribeiro%2Fcourses%2Fengr332%2FHandouts%2Fnyquist-margins.doc&ei=mF_LU6_HCcqN4gSploCwAw&usg=AFQjCNH3LvOuEJC4iAxjwaW_O6UUAmZuCA&bvm=bv.71198958,d.bGE

http://www-control.eng.cam.ac.uk/gv/p6/Handout6.pdf

http://ee.eng.usm.my/eeacad/nasiruddin/ARCHIVES/EEE350/lecture%20notes/nYQUIST%20PLOT.pdf

http://mmae.iit.edu/~mpeet/Classes/MMAE443/443Lecture23.pdf

http://inc.kmutt.ac.th/course/inc341/BP08/341lec12.ppt

http://seit.unsw.adfa.edu.au/staff/sites/valu/teaching/ct2/nyquist.pdf

http://flyingv.ucsd.edu/krstic/teaching/143b/finals/Final13Sol.pdf

http://homes.et.aau.dk/yang/DE5/CC/mm9.pdf

http://www.me.ust.hk/~mech261/index/Lecture/Chapter_9.pdf

http://wolfweb.unr.edu/~fadali/ee370/Nyquist.pdf

http://www-users.aston.ac.uk/~norriswt/ControlNotes/Nyquist%20Stability%20Formulati.pdf

http://homepages.wmich.edu/~kamman/Me360FrequencyDomainAnalysis.pdf

http://csindulkar.tripod.com/nyquistcriterion.pdf

https://inst.eecs.berkeley.edu/~ee128/fa11/Homework/ps6sol-v2.pdf

http://robotics.mem.drexel.edu/mhsieh/Courses/E58_S08/Notes/controlTheory_19.pdf

http://mmae.iit.edu/~mpeet/Classes/MMAE443/443Lecture23.pdf

http://www.wolframalpha.com/examples/ControlSystems.html

http://www.engr.usask.ca/classes/ME/431/notes/Note_15-2006.pdf

http://mathlets.org/mathlets/nyquist-plot/

http://lpsa.swarthmore.edu/Nyquist/Nyquist.html

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

http://shiwasu.ee.ous.ac.jp/matweb_cs/help/english_st_sp_f_help.htm

http://www.bisonacademy.com/ECE461/Lectures/31%20Nichols%20Charts.pdf

http://my.safaribooksonline.com/book/electrical-engineering/electrical-controls/9780471249061/6-techniques-for-determining-control-system-stability/sec6_11_html

http://www.bisonacademy.com/ECE461/Lectures/31%20Nichols%20Charts.pdf

https://www.calvin.edu/~pribeiro/courses/engr315/lectures-notes/chapter-8-9.ppt

http://ee.eng.usm.my/eeacad/nasiruddin/ARCHIVES/EEE350/lecture%20notes/Nichols%20Chart.pdf

http://web.mit.edu/klund/www/papers/ACC04_threed.pdf

http://www.cambridge.org/us/features/chau/webnotes/chap8nichols.pdf

http://www.che.utexas.edu/course/che360/lecture_notes/chapter_14.ppt

http://profesores.elo.utfsm.cl/~jgb/nicholsI.pdf

http://diegoregruto.com/P12.pdf

http://personal-pages.ps.ic.ac.uk/~nina/Research/PDFPapers/ControlLoopStabilityArticleMarch2007.pdf

http://www.freestudy.co.uk/solutionsd227/2003/q2.pdf

http://profsite.um.ac.ir/~karimpor/control/lectures/lec26_control.ppt

http://control.ee.nsysu.edu.tw/Class/%E8%87%AA%E5%8B%95%E6%8E%A7%E5%88%B6%E7%B3%BB%E7%B5%B1/Chapter%2008.ppt

http://www.control.lth.se/media/Education/DoctorateProgram/2012/Delays/Lectures/lect01.pdf

http://web.iitd.ac.in/~janas/courses/eel301.htm

http://www.chemeng.queensu.ca/courses/CHEE434/lectures/documents/CHEE434_notes_nyquiststability_2011.pdf

http://www.znu.ac.ir/data/members/pirmohamadi_ali/Control/final_Exam.pdf

http://profs.hut.ac.ir/~khodabandeh/courses/linearcontrol/LinearControl_HW8.pdf