"Combination" Properties

Why doesn't MyFlightbook support the ability to explicitly log "combination" properties, such as "Solo Cross-country" or "Night PIC"?

I generally strongly avoid "combination" properties for a few reasons:

• Most importantly, this can generally be computed.  So a given flight’s “Cross-Country Instruction Received”, for example, is computed as MIN(Dual, Cross-country).  It’s an approximation, but in practice (for reasons described below), it’s way more accurate to do this than logging explicitly.
• Explicitly logging can lead to ambiguities or outright errors.  E.g., suppose you have a flight that has 2 hours of total time, 2 hours of cross-country time, and 1 hour of night.  It’s pretty obvious that this flight has 1 hour of night-cross-country (see above).  Now consider if it were possible to explicitly log "Night Cross-country."  If you logged 1.5 hours of night-cross-country, then it’s clearly an error.  If you log 1 hour of night-cross-country, then you just wasted your time.  And if you forgot to log night-cross-country, then should I count an hour of night cross-country or not?  (Probably yes since it’s obviously there).
• The number of possible combinations of PIC, Night, Cross-country, Solo, and Instruction grows very rapidly, making data entry insanely cumbersome (a given flight can have lots of these combinations), and lead to you forgetting to log all of the possible combinations that applied to a given flight.

For these reasons, I try to limit data entry to the “independent variables” (solo, night, pic, cross-country, dual received, etc.) and compute the combinations as needed.

I do these computations in the 8710 form, as well as in the various ratings-progress screens.