In the Real Book, diminished chord symbols are like D#o7. In the list of chords recognized by BiaB, there's only "dim", as D#dim, but no "dim7"

https://www.pgmusic.com/tutorial_chordlist.htm

Is "o7" on the chart really the same as "dim" in BiaB? (It sounds okay, but I'm no expert.)

You can type in Cdim7 as in #1 or right click on a beat, click on chord, select the root, then from the drop down menu select Dim7.

Also be sure to click on options, preferences, display, and check treat dim chord as a dim triad .............

Yes they are both ways to write a diminished chord, and then the number after the dim represents the note in the chord that is lowered. The "o" is a degree symbol, but a degree symbol is not as easily typed as it is written. That's why in Band-in-a-Box it is programmed to recognize the word "dim" so that way it is clear what the chord is.

A little theory, and a little history:

The nature of a diminished chord is that the series of minor third intervals can continue right up into the next octaves. For example, C, Eb, Gb makes a Cdim chord. Most music outside of the classical world would consider adding the Bbb (enharmonically A) as the seventh. Then the magic of the diminished chord is that you continue up using the same four pitches in the next register. Start again with C etc. so there are really only three diminished chords! They can start on C, C#, or D before the notes repeat.

BIAB used to assume you wanted a Dim7 when you wrote Dim. This is likely owing to its origin for doing jazz fakebook tunes. Some years ago, and I’m going to make a rough guess of about 15, we asked that we be able to distinguish between the two. In other words, if we wrote Dim we did not want to hear the double-flatted seventh.

PG Music granted our wish and gave the options Mario pointed out.

The preference to display as dim7 is what I needed. Thanks.

I'm glad I could help.