The problem is how do you advise a measure which everyone has access to. We did try to source a suitable measure but one doesn't seem to exist and most people have fingers available.
Although 'a pinch' sounds arbitrary - it isn't. When we formulated Nutrobal we did a survey and had dozens of people take three pinches and weighed them. Done every day by normal people the variations iron out and a suitable dose is achieved, we based the formulation on the average/normal human pinch and there is a considerable safety margin built in by nature.
Provided that people are sensible we all know what a pinch is - not absolutely as much as you can pick up by flattening your fingers to the first knuckle just a normal pick up a bit.
We have sold Nutrobal since 1989 and NEVER had an issue with overdosing.
The other side of the 'problem' is that if you go for a more 'dilute' formulation such as the dog vitamin products the amount of material goes up and you can use a small blue spoon or whatever but the volume of powder is so great that the animals don't eat it - just as we can't eat 6 dry cream crackers.
Tortoises walk through their dinner and take the Nutrobal with them some days, others they simply miss it, others they take the lot. Nature is wonderful at achieving balance out of whatever we throw at it. Even the small tortoise isn't a problem because a tiny/small pinch is fine, we always feed to excess so Nutrobal and food are left behind.
As part of answering the question, we need to look at how tortoises are fed, and how they eat. In general more food is given than they eat, they then walk through it munching on what takes their fancy, so some powder is missed, stuck to the head, carapace or simply left on the ground. Care needs to be taken with feeding hatchlings as they are 'programmed' to eat as much as is available to allow for the days when food isn't around. This can mean that they overeat generally if given ad-lib food, this will cause a rapid abnormal growth rate and often leads to lumpy shell etc. One answer is to feed just once aday with high fibre, weedy plant material, do NOT overfeed.
So for supplementing small tortoises just use knife-point type amounts of Nutrobal to sprinkle on food and give it on alternate days, on the other days use Calci-Dust sprinkled on the food. The other way of doing it is just to have in mind the term 'lightly dusted'.
Again, since powdered vitamin supplements are used on the freshfood (they fall off seed) and we generally end up throwing a large amount of that away there is an inbuilt wastage element. ie you dust the fresh food, mix it well in and will find that the birds are selective. They eat some they leave some, and you end up throwing some of the food away.
Rough bird weights are as follows:
1kg = one of the larger macaws (Hahns, Spix are smaller)
= 2 African greys or 2 amazons
Rough weights of some smaller species (from Coles 1997):
zebra finch 10-16g
pekin robin 26g
For these birds obviously use smaller pinches, knife points or consider using the supplements on alternate days (equivalent to halving the dose). In colony situations it isn't a problem since the multiple birds equate to one big bird!
For the single, non-breeding bird we also supply liquid supplements for addition to the water. see BSP vitamin drops and Zolcal D liquid calcium.