What exactly is Ekagata. (One pointedness)?

[auto]

these five strings of sensuality, that is sensual pleasure.

What about the pleasure of the mind? (sixth sense?)
Isn't Pithy and Sukha related to mind, not to the five strings of sensuality?

the full sentence is,

Whatever pleasure or joy arises in dependence on these five strings of sensuality, that is sensual pleasure.

pleasure rises in dependence on these five strings of sensuality. Pleasure is object of mind.

If you want to sit on a chair for to get an ease, that is unskillful quality of mind. If you sit and want to change the position to feel more comfortable, that's also unskillful.
Sensual pleasure is what arises in dependence on changing sitting position. And during that moment you are focusing on the manasikara.

Now there is the case where a monk — quite withdrawn from sensuality, withdrawn from unskillful qualities — enters & remains in the first jhana

the desire what arises is sensual desire, an affliction and that is perception of sensuality. What formerly were sensual pleasure now is sensual desire and has manasikara included.

The rapture and pleasure rising from withdrawal doesn't have affliction nor demanding. You got to get that your object of mind by using discernment its done by being quite secluded from unskillful mental qualities.
Bit by bit getting aquintated to that dimension and acquiring confidence.

https://en.wikipedia.org/wiki/Ayatana

Buddhism and other Indian epistemologies[8][9] identify six "senses" as opposed to the Western identification of five. In Buddhism, "mind" denotes an internal sense organ which interacts with sense objects that include sense impressions, feelings, perceptions and volition.[6][10]

sixth sense include the other five. Its prolly you can't seclude yourself from sixth sense like you could with the 5 senses.

[SarathW]

If you want to sit on a chair for to get an ease, that is unskillful quality of mind. If you sit and want to change the position to feel more comfortable, that's also unskillful.

I am not sure of this.
Buddha used to sit on a pile of grass to make him comfortable.

[Virgo]

Ekaggata cetasika:

http://www.vipassana.info/cetasikas8.html

Kevin...

[auto]

If you want to sit on a chair for to get an ease, that is unskillful quality of mind. If you sit and want to change the position to feel more comfortable, that's also unskillful.

I am not sure of this.
Buddha used to sit on a pile of grass to make him comfortable.

When you are doing sitting(or some other position, walking etc) practice then there is urge rise what wants you to quit(doesn't have to be in this way, there is a lot of versions) practice. By answering the call of that urge you used it up and it will rise again to interrupt your practice. It seem you don't notice that urge, it is basic practice instructions what you can read from Mahasi Sayadew booklets, it is to notice your "wantings"
and even if you notice them you also need respond correctly to them and sense and catch the urge before it arises.

Any type of practice are for this one thing if you do it right, then you get into a mind there you can discover certain type of concentration, it is not available for you unless you overcome that urge (volition or being idk doesn't matter).

And due to have to cultivate, its not happen over night it takes months of correct practice and it is without confidence at first, you don't know what you doing at that time and also when you attain that concentration you still won't know what you doing and don't have completed to have confidence.