I'm a guy, but do the 2 ladies in my avatar count?
I'm going to add my 2 cents in on this scale subject.
Karma, you seem to be revolving around two concepts in error. Accuracy and precision. You can precisely measure small parts, but the accuracy of the entire bike comes into question, error is propagated, and this concerns you?
As you have noted, the cost of a balance scales with precision. So for example, I have solenoid based balance in my lab which has a useful range of 200g. And is precise to 1/100 mg. So theoretically I could weigh 199.99999g accurately and precisely. This balance is too costly for any normal usage. The cost the service contract on this balance is more then my bike.
Error propagation in addition, how does it affect accuracy? Lets say you had weights of two components with absolute uncertainties, 1000+/-5g and 10+/-1g. The error would be 1000+/-(0.5%)g and 10(10%) relative uncertainties. Added together they would be 1010(+/-x) were x is the square root of the added squares of the absolute uncertainties, i.e. 5.1g So the result is 1010+/-5.1g. As you can see from this example, the heavier weights propagate their error more (regardless of the relative uncertainty). So to be practical, you would want a balance that is capable of the most accuracy with the largest capacity for your object.
Your example of 10*10g error, is 100g error, your right. But you forgot to mention the fact the number you were measuring is now 10x more precise! In general, the more measurements you have, the more precise your number is, not the other way around. The accuracy of any weight is solely dependant of the quality of the balance, and if it’s properly calibrated. That’s why you don’t weight little tiny things on big balances, and big heavy things in tiny balances.
I hope you are comfortable accepting error. It sounds like you’re about to put down some cash, and I hope you find a good deal. Good luck. Sorry to hear about the $30. Let us know what you find.
BTW, cleaver with the Buckyballs, i.e. spherical graphite. There are a lot of people (like me) who are trying to use things like buckyballs as structural components in synthetic resins. Unfortunately buckyballs do not really reinforce in the same manor carbon/glass fibers do, and the cost of getting them into a process-able matrix is prohibitive. Exfoliated clay structures are showing some promise as nano-reinforcements, but their mechanism of reinforcement is again different then carbon/glass fibers, they restrict the chain movements of the polymers, this great for making strong materials, but really becomes a big pain in the ass to make parts from them. The future if synthetic resins will someday outperform carbon fiber composites, but for now, we will ride our bikes without Buckyballs.