Simply, An/Ci curve could be obtained through a series of Ci and its corresponding An values. The gas exchange measurement could be conducted first at a Ca of 400 ppm followed by stepwise decreased Ca to 50 ppm (e.g. in six steps at a 50 ppm intervals). When all these measurements are done, returning Ca to 400 ppm to restore the original An, and then, increasing Ca stepwise to 2000 ppm.

Things should be considered:

1.The activity of Rubisco could be reduced under low CO2 concentrations if you wait to long.  It is said in the literature that each data point should be finishd in 3 to 5 minutes and it is not neccessary to wait for the stable status. 

2. Check the leakage of the cuvette in different CO2 concentrations.

3. Do some pre-experiments to find the CO2 concentration under which the limitation of photosynthesis starts changing from Rubisco-actoivity-limited phase to RuBP-regeneration-limited phase. It helps when you want to estimate mesophyll conductance.

The An/Ci curve gives not only  the readout of parameters, such as An, gs, Ci, and E, but also can be used to estimate mesophyll conductance, Cc, Vmax, and Jmax.

Papers I recommand:

1.CJ Bernacchi (‎2002).Gas exchange measurements, what can they tell us about

the underlying limitations to photosynthesis? Procedures

and sources of error.

2.S. P. Long1, and C. J. Bernacchi. (‎2003) Temperature Response of Mesophyll Conductance. Implications for the Determination of Rubisco Enzyme Kinetics and for Limitations to Photosynthesis in Vivo. 

3.Flexas J, et al. (2007) Mesophyll conductance to CO2 in Arabidopsis thaliana.

4.THOMAS D. SHARKEY, et al. (2007). Fitting photosynthetic carbon dioxide response curves for C3 leaves.

Zhenyu had given real insight into gas exchange estimate.  there is small application to get all the A/Ci estimates, called Photosynthesis assistant. The application can be downloaded at http://www.scientific.force9.co.uk/photosyn.htm

All depends on the experiment design. The curve should be taken at saturating light and on leaves without water stress for the time lenght that is required to equilibrate at each CO2. Uneven stomatal opening and low stomatal conductance may make difficult to reach high CO2 levels. More a synthetic gas mixure (N2 97%-O2 2%-CO2 2000vpm) with low oxygen may be applied for extimating photorespiration and other parameters like internal conductance. At end the infos may be useful in different specific questions . Licor has got several apps and examples. https://www.licor.com/env/products/photosynthesis/LI-6400XT/software_downloads.html

There are couple Aci curve fitting tools. http://landflux.org/Tools.php and http://www.leafweb.org/information/about/

I agree with Zhenyu Yung procedure.

The commentary written by Sharkey (2015) concluded the calculations (such as photosyn assistant, PCE calculator, etc.) and the use of potential parameters (Vcmax, J, TPU, Rd and gm) estimated from A/Ci curves.

http://onlinelibrary.wiley.com/doi/10.1111/pce.12641/abstract;jsessionid=15EA9CD722C6F661A306E3BAB2AFDD6A.f02t03

I am highly grateful to all of you for knowledge sharing.

So no one would try this method??

New Phytologist (2017) 213: 1543–1554

http://onlinelibrary.wiley.com/doi/10.1111/nph.14260/abstract

The method proposed by Tsu-Wei Chen is a professinal and of great significance work both for experts or abecedarians. The EXCEL calculator bring us a lot of convenience. Before using the excel sheet, we need to install first the solver Add-in in excel. It is always available and we just need to activate it. To check if the solver is already install, open excel and go in data. The solver appears there in all excel versions. If not, go to File --> Options (or Excel options) --> Add-ins . we get here the list of available add-ins. In Manage, choose excel add-ins and click on GO. In a new window, select Solver. Thereafter, we will be able to follow the steps and find the GRG nonlinear and so on.

Llorenç Cabrera-Bosquet the method that you suggest only considers the C4 metabolism or can be modified to C3 metabolism?

Tsu-Wei Chen, I am using the method suggested for your team. However, I have not clear why it is not possible the Rd calculated? Excellent work. Thanks.