Your over-riding requirement appears to be that the file be human-readable. You are "settling" for a string representation, which is fine for a Boolean, but perhap less satisfactory for Dbl data (I forget how many digits of precision -- around 15? -- are carried in the Dbl format). Depending on how you format the representation of the Dbl, you'll get an "N-digit" approximation of the value (which, admittedly, is a 52-bit "approximation" to a real number) or a hard-to-read string of (possibly unnecessary) digits.
There is a way to "have your cake" (Human-readable) and "eat it, too" (retain native representation) -- instead of using LabVIEW's "Spreadsheet" File I/O functions (which write String representations/approximations of your data), you could, instead, save the data in an Excel WorkSheet. An Excel cell can "adapt" to the type of data stored in it -- if it is a Dbl, it can be held in "human-readable" format (with whatever display precision you desire), yet retain all of the bits-of-precision "under the hood".
Your task is a little more complicated by the (apparent) need to accept either Boolean or Dbl, but with the type not known, apparently, until run-time (which appears to be why you went through all of the shenanigans with Variants). Something you might consider, if this situation should happen again, is to write a Polymorphic "Store" function that can handle both a Boolean and a Dbl input (look up Polymorphic VIs in LabVIEW Help).
You can use the LabVIEW Report Generation Toolkit (if you have it) to create true Excel Worksheets. You can use the Excel Easy Table VI to handle the placement of a "table" (a 2D array of Text or Dbl) into Excel. Right away, however, we run into two (minor) problems -- Easy Table, though it is polymorphic, only accepts Text or Dbl data, so we'd have to change the Boolean to a TRUE/FALSE text string. Second, what do you do if you need to save single values (as you may not know whether you are saving a Boolean or a Dbl)? Simply -- Build Array twice will turn a scalar -> 1D array -> 2D array (albeit a 1x1 array). The final question is how do you control whether you are writing a row or a column of data? Use the Start input and two "Next Cell" outputs (and Shift Registers) to either make "next cells" line up "top-right" (in a row) or "bottom-left" (in a column).
This may be much too much effort, gross overkill, but since you "love math" (as do I), seem to be "getting into" LabVIEW (oop, I didn't mean to make a pun), and seem interested in some of the nooks and crannies, I thought I'd comment.
Bob Schor
