How to set "characters" as "missing values"?

[#1]

My table on JMP has a column that contains both numbers and characters. The table lists down products, and this column records the minimum requirement for a specific performance test. Therefore, the cells of the columns could store one of the three:

- a numerical value;

- "N/A" when the test is not required to be performed on a specific product (entry);

- two alternative numerical value (e.g. 4.5 if... or 5.5 if....).

If I leave the data type of the column as character, when plotting a histogram, this looks quite messy: the entries are not ordered as I'd like them to, nor the different numerical entries are in scale). If I change the data type of the column into Number, all the cells that contains text are emptied.  

Is there a way I can convert the data type of the column as numbers, but tell JMP to consider any text entry as an empty cell? (Without actually deleting the info in the cell?) 

[#2]

Not my knowledge and in my opinion "wrong" to have column data type as numeric while it would still contain character data. Depending on the data you have:

1. Create new column with the values copied over and change that to numeric. You could also hide/exclude old/new column depending on what you are doing.
2. Split the data so you have one product on one row and then multiple columns depending on what the one of three values mean

Option two would most likely be better in a long run (again depending on the data and purpose).