Please find my comments in the enclosed document.

GENERAL COMMENTS

The authors present an open hardware low-cost DIY chamber measurement system for to estimate soil CO2 effluxes and compare it to much a much more expensive a state-of-the-art system. The manuscript addresses the problem that the main source of uncertainty associated to chamber measurements is not associated to the technology used, but to spatiotemporal sampling limited by available resources. The low-cost approach suggests that it would be beneficial to sacrifice some quality of a single measurement to favour quantity and overall quality in terms of more measurement plots per site and more GHG flux sites overall. The use of parametric chambers promotes the responsibility of the researcher to minimise bias in the data. This is important because while today producing numbers is easy, but producing good data is as hard as ever. Therefore, the manuscript facilitates, in my opinion, much needed paradigm shift in GHG flux research.

As the authors report, several low-cost DIY systems have been introduced recently. However, this particular system is completely new. It new featuring parametrised chamber design, allowing the system to be customised to be used in different environments. The manuscript contains only little data, but it is enough to show that in good conditions the system works at least as good as expected. The evaluation of the performance as an automated system in field would require extensive measurements over a longer period of time. The presentation quality is good.

The schematics and code are provided for building a working chamber. An OnShape account is required for the access.

Overall the manuscript has a high value for scientific research, but especially for people studying GHG fluxes outside the Academia. The methods used are sound, presentation is clear, language is appropriate and for the most part the experiment is explained in an understandable way.

SPECIFIC COMMENTS

It is not instantly clear how the transient change in concentration in the chamber was actually measured. In Eq. (2), what are the measured variables?

TECHNICAL NOTES

Figure 7. I don't understand why D[CO2] is shown here instead of the actual [CO2] with Y-axis starting from e.g. 400ppm?

258-261: Or the measurement length could be shortened.

283-285: Another option would be to introduce constant air mixing. As long se the conditions do not change, there should not be gas accumulation/release (storage change) effects. 

290: of a any -> remove "a"

297: Please specify here what you mean by high-frequency. Spatial, temporal or spatiotemporal?

309: The link seems to be wrong here. It is possible to navigate to the correct page (https://github.com/alexnaoki/SoilGasFlux; I assume) from the link in the references, though. Opening the chamber schematic requires an OnShape account that I did not want to create, and I will not comment on that.