To make a Diminished chord the 3rd is lowered a half-step but the 5th is lowered a half-step also.

Using the C chord we know the note's are C-E-G. You can also remember it as a "1-3-5 in C".

If the 3rd and 5th are both lowered a half-step each the note's for a C dim. are C-Eb-Gb. Easy to do maybe not as easy to chord but that is what practice is for.

Let's take the B maj. as another example using the root note's B-D#-F#.

Lowering the 3rd a half-step makes the D#, a D, and lowering the 5th a half-step makes the F# an F. A B dim. chord has the note's B-D-F.

If at any time you find yourself having trouble doing chords, maybe going back to "Intervals" and "Sharps and Flat's" will help clear the dust.

SUSPENDED CHORDS
(sym.-Bsus.,Gsus.,etc...)
l-3-5+4th tone

This is the last (hallelujah), section in the "Chord Structure" chapter.

The numbers chart reads that to make a suspended chord from the root, the 4th tone has to be added.

The root for a Gma. or "1-3-5 in G" is G-B-D, adding the 4th tone gives us the note's G-B-D-C.

Using a Dma. root, the note's are D-F#-A, and adding the 4th gives the note's of a D sus. chord as D-F#-A-G.