If the TDS doesn't list the weight/volume I pour up a liter of the product and do that math.

If I'm mixing more than a couple hundred ml of paint I use the volume method. If you just need 30 ml of epoxy 2K primer to touch up a spot where you burned through to bare metal the skill of mixing by mass (weight) is very convenient.

My drawback is that the best balance/scales I can afford are not sensitive enough to mix the hardener in a blob of body putty or filler. You just can't do 2g on a kitchen scale.

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84 300SD
85 380SE
83 528e
95 318ic