Yeah, it's a simple wooden rod, ~3mm diameter. The initial plan was to design and print a 3d part and this was a quick test. It worked so well, that I didn't bother changing it
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/xcheesy.gif.pagespeed.ic.KPzuH4J-TG.png)
You could add one or two decades to the design or just populate the PCB differently (e. g. for 0.1 Ohm ... 100 kOhm). That being said, the big issue is the contact resistance of the switches/relays. It might vary with switching voltage/switching current/age/temperature. The contact resistance of the EC2 relays I used in my design is fairly high compared with a resolution 0.1 Ohm (and even more so for 0.01 Ohm): I measured about 0.025 Ohms for both poles in parallel using my Agilent 34401A @ 1 mA measurement current in the 100 Ohm range. (Edit: This is an average of many relays in series using 4W measurement, determined during the calibration procedure.)
Depending on the topology used there might be a varying number of contacts in the signal path. As can be easily seen in the diagram, with the topology I've selected the deviation varies when changing from odd to even resistance values and vice versa. Actually, the number of relays in the signal path of a decade is 2* for even values and 1 for odd values (*in parallel with a resistor; at least for my design with 1 Ohm the improvement caused by the parallel resistor is insignificant). The deviation caused by the changing number of switches in the signal path is so large (i. e. ~0.025 mOhm) that I wouldn't feel comfortable going below 1 Ohm with my design. I would recommend using a different topology (meaning more relays and hence higher cost and other technical differences) and/or relays with lower contact resistance for the decades below 1 Ohm (maybe even for the 1 Ohm .. 9 Ohm decade).
Maybe also take a closer look at my documentation (see links above, hackaday or my personal page). There I have described many aspects of the design, including the problem with the contact resistance, which topology I used (and why) etc.
The front and rear panels are simple prototyping aluminum PCBs. The white solder mask is reasonably uniform. I ordered the minimum quantity of 5 PCBs and there are slight differences (e. g. visible scratches, silk screen uniformity etc.) The black silkscreen as well as the rectangular cutouts are not 100% perfect, but more than good enough in my opinion, not only, but especially if I consider the pricing of cheap prototyping boards. Again: Not perfect, but I'm more than happy with the result and this obviously depends on the PCB manufacturer.
Haven't calculated the cost yet, but I think it's a good idea to do so. I'll give you a number soon
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/xsmiley.gif.pagespeed.ic.R8GFI-pF6f.png)
Designing the PCBs was relatively quick & easy, writing the software was much more time consuming and - quite franky - sometimes not that much fun. The project took me many hours, many more the I initially planned - but it's more capable than I initially planned
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/xcheesy.gif.pagespeed.ic.KPzuH4J-TG.png)
How many hours though, I will never know - sorry.