Anglinarcher - AndyUK may well be a beginner when it comes to lure building, but he is certainly not new to engineering, and fully understands what I am talking about, otherwise I would not have embarked on this tedious and time consuming project. The idea is that I take care of the complexities of the many calculations, leaving the builder with a few measurements to make and a couple of numbers to play with.
My 2DP scale is repeatable, and that is the most important factor, and yes, I have a certified 500g mass. I also have a250ml class-A HERMA graduated measuring cylinder, and with 1cc being less than 1mm I will be calling BS on your claim of 1/10cc. I stick by my claim that the best you can hope for is an accuracy of 1cc and add to that a tolerance of =/+ 0.5cc.
Yes, the larger the sample the better the accuracy, we should always use the largest sample possible.
The reason I went down to 2DP for my gram scale was that when I was experimenting with neutral buoyancy several years ago, I found that 1DP was right on the edge for a 1DP scale. We are looking for an accuracy of 1/200th of the volume of the lure to even getting close to the accuracy required, and as you know, there are tolerances with each measurement made; resin, filler, internal hardware, external hardware, ballast. If you are lucky then the tolerances will balance each other out, but that does not always happen. And then, you have top coats to deal with. For larger lures, even a 500g scale is useless for doing water displacement measurements.
I am sure you will enjoy playing with the spreadsheet, and I will send you a copy once the beta testing is done.
Dave