I live in the U.S. so I must confess I was/am totally ignorant of what a "doubler" is and how it is used; so I did a quick google search to see if I could learn something. I found
this site which seems to give a pretty good description (please correct me if this is not what you are talking about).
With that as my understanding; I am not sure what you want to do. Are you trying to: 1.) make your own doublers (a finished product without nicotine)? Or: 2.) are you trying to figure out how to use a commercially purchased doubler as an "ingredient" in the Juice Calculator (adding nicotine concentrate to the doubler to dilute it to its intended flavor strength and raise the nicotine to the desired level)?
If 1.); then:
You are basically creating a recipe with 0 (zero) nicotine and the flavors at twice their intended strength. So to do this you would set your "Target Nicotine" level to 0.00 and double all flavor concentrate percentages. For a "tripler;" triple all flavor concentrates. PG/VG (specificly higher VG) ratio will be limited by the increased percentage of flavor concentrates and what carrier(s) are used in each flavor concentrate (typically PG).
If 2.); then:
You would want to enter your "doubler" as an ingredient. Here is a sample of what it might look like:
View attachment 639483
The important parts to include (highlighted) are:
-Name
-Ingredient Type
-PG/VG Percentages
-Default Percentage (Optional: this just simply sets the default value with which it is introduced to the recipe. You can still change this value within the recipe.)
-Cost (not highlighted)(Optional: only required if you wish to know cost of finished recipe.)
Then; create the recipe (dilute the doubler down to vapable strength and add the nicotine). It will look something like this:
View attachment 639495
Note the critical info:
1. Desired nicotine level
2. Desired size of finished recipe
3. Nicotine base you are using (I followed recommendation of using double the desired nocotine strength for this example)
4. PG and VG lines set the desired finished PG/VG ratio
5. Your doubler used as an ingredient (what we created in the previous example). Use 50% for a doubler and 33.33% for a tripler.
Now notice what happens if we change our nicotine base:
View attachment 639499
By changing from a 48mg/mL 50% PG/50% VG nic base, to a 100mg/mL 0% PG/100% VG nic base, notice how the amounts change for nic, PG, and VG.
If that is more than you want to do; I did also come across this "doubler calculator" during my same google search:
E-LIQUID DOUBLER CALCULATOR
http://doublercalculator.com/
I hope something here answers your question. If I missed it; please feel free to sing out.