Access: Calculating weighted numeric grades from letter grades for multiple fields - ms-access

Question

I need to calculate a weighted grade from 3 criteria (Health, Structure, Form) for each tree. Each tree has a letter grade (A-F) for each of the criteria. The overall grade for each tree is weighted by the criteria.
I have a TREE TABLE with fields: tree #, a health letter grade (A-F), a structure letter grade (A-F), and form letter grade (A-F))
I have a GRADING SCALE TABLE with fields: letter grade (A-F), numeric grade (1-0)
I have a WEIGHTED TABLE with fields: criteria (health, struc...) and weight (.2, .6..)
I have a one-to-many relationship from the GRADING SCALE TABLE [letter grade] to each of the criteria on the TREE TABLE [health letter grade], etc. Many trees can have the same grade.
When I first tested a query showing the numeric grades for each tree, but this resulted in triple records for each tree and these were not the correct values.
I figured I would step the process and ran a query using the switch function, which provided the correct numeric grade for each tree for each criteria (Yay - this was based on a similar post that calculated numeric grades from letter grades)
I used:
HealthNum: Switch([Health]="A",1,[Health]="B",.75...,True,"Missing a grade")
BUT, I am struggling to run a query to calculate the weights for each criteria and the ultimate weights.
I tried for each of the tree criteria: HealthWtd: [HealthNum]*[Criteria_wt]; where the criteria field was set to [Criteria]="Health"
When I set [Criteria]="Health" and I put in the [Criteria]="Structure" in the OR position, I end up with two records for each tree. One record has a correct health weight and an incorrect structure weight, while the other record has an incorrect health weight and correct structure weight.
Some of the caveats: the grading scale and weights are likely to change from time to time, so I would rather use a relationship over the switch function. My boss has disliked the use of excessive nesting.
I feel like this should be an easy task and cannot for the life of me figure this one out.

Answer 1

With current table structure, either hard code weight factor in query expression or use DLookup() to pull correct Weight factor from table. Could also use DLookup() for Scale.
Example for Health:
DLookup("Weight", "Weighted", "Criteria='Health'") * DLookup("Number", "Scale", "Letter='" & [Health] & "'")
Tree table is not normalized. If it were, could join to Scale and Weight tables to properly associate records and calculate weight. Then a CROSSTAB query could produce the horizontal output.
Normalized table which could be joined to other tables:
+---------+-----------+-------+
| TreeNum | Criteria | Grade |
+---------+-----------+-------+
| 10 | Health | A |
+---------+-----------+-------+
| 10 | Structure | B |
+---------+-----------+-------+
| 10 | Form | C |
+---------+-----------+-------+
| 12 | Health | B |
+---------+-----------+-------+
| 12 | Structure | B |
+---------+-----------+-------+
| 12 | Form | D |
+---------+-----------+-------+