You don't need to be too fussy about the 1/8" bit -- I found the tines on my fork are about this thick, so used that to calibrate the mandoline. The first time I did this though, I just used a chef's knife and ballparked it, and that works just fine too.
This dish brought back a quirky memory about my dad. He used to prepare something like this in foil on the bbq, and while he was chopping spuds he'd happily much away on raw chunks of them. This always creeped me out for some reason -- I'm not sure why a raw potato would be any different from a raw carrot. I even tried it, and they taste ok. But I remain on the *shudder*
Peace to you all this new year, and all the best in the kitchen and any where else you happen to be!