Question: Listen From 00:56
[![enter image description here](https://i.stack.imgur.com/X68RF.jpg)](https://i.stack.imgur.com/X68RF.jpg)

The [E] part is in C Major key

and I can't understand the C#m7-5 chord at bar 3

what is this chord ? 

Where did it come from? and what is its function ?

Answer: 
Depends on the Time Signature.
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The first grouping would be ideal in Time Signature with minim beats, the beats are upheld but the subdivision of the beat aids in the reading of notes.

The second grouping is correct when you have crotchet beats because there is a grouping rule that says you subdivide the beats when you have semi-quavers in Time Signatures with crotchet or dotted crotchet beats.
A performer would play both versions the same way (you wouldn't accent the first note of every group or anything like that!). The differences are more for ease of reading / comprehension rather than performance instructions. 

The top example (Hanon) might be grouped as 8-note sets to show where the finger pattern repeats (you use 1234 5432 / 5432 1234 over and over again, just starting on a different note).

The second example makes it a bit easier to see where the crotchet beats are. (4 per bar). You could group them like the first example, but it might be slightly harder to read that way.