That will likely work for the length or width of boards, but what about thickness? Mark out a mortise and tenon on a 19mm thick board with that technique and tell me how it goes.
This is the kind of shit I’m talking about. You see these kinds of “Nuh uh, it’s not a problem, you just learn all these hacky workarounds” excuses out of the inch-ounce crowd, where you “just have different measuring cups for that” or “our butter packaging has tablespoon markings on it” but in the wood shop it’s the other way around because the physical tasks are inherently easier to express as fractions rather than decimals, so I’m the one saying “I just measure it with my tape measure or combo square or ruler and it’s right.” and the metric crowd keep going “Nuh uh, it’s not a problem, you just learn all these hacky workarounds.”
That will likely work for the length or width of boards, but what about thickness? Mark out a mortise and tenon on a 19mm thick board with that technique and tell me how it goes.
This is the kind of shit I’m talking about. You see these kinds of “Nuh uh, it’s not a problem, you just learn all these hacky workarounds” excuses out of the inch-ounce crowd, where you “just have different measuring cups for that” or “our butter packaging has tablespoon markings on it” but in the wood shop it’s the other way around because the physical tasks are inherently easier to express as fractions rather than decimals, so I’m the one saying “I just measure it with my tape measure or combo square or ruler and it’s right.” and the metric crowd keep going “Nuh uh, it’s not a problem, you just learn all these hacky workarounds.”
Or you can do a division and that’s it.
19mm / 3 = 6.3333mm. Come on over here and show me the six point three three three three millimeter line on my metric tape measure.
2" / 3 = 0.666666666 Show me that point in you tape measure 😜
And both cases can be fixed by just skewing a little the tape (19 mm -> 21 mm and 2" -> 2.1". Close to 20°)