The only way to know for sure how many units of Botox are injected is to ask your provider. You should be able to trust him or her. If you don't trust him, you should go elsewhere, but there are several explanations that might account for the variances you're noticing.
The Botox comes to us as a freeze-dried powder in a glass vial. Each injector reconstitutes the powder with a saline solution. They can put in 1, 2, 2.5 or even 4 ccs of fluid. The more saline, the more dilute it will be and the more fluid will need to be injected to achieve the desired effect. One way is not better than another - they are just different and each injector will have his/her preferred method.
If your previous results appeared in 24 hours, this may have been a more concentrated solution (less saline per unit of botox). It is normal for botox to take 3-7 days or more to see the full effects.
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