What it is
Chaturthamsha, also called turyamsha, divides each sign into four equal parts of 7°30′. The four parts go to the four angles counted from the sign: the same sign, the 4th, the 7th and the 10th.
How it is calculated
Rule: 0–7°30′ the same sign, 7°30′–15° the 4th from it, 15–22°30′ the 7th, and 22°30′–30° the 10th.
Example: a planet is at Aries 17°. 17° is in the third part (15–22°30′), so it goes to the 7th sign from Aries, Libra. In D4 the planet is in Libra.
What tradition looks at in it
Parāśara links the chaturthamsha to fortune, and tradition also reads home, land and the comfort of one's dwelling in it. Astrologers look at the lord of the 4th house, the D4 ascendant and its lord. Mars is the traditional significator of land and Venus of comforts, so their placement is noted too.
How much the birth time matters
On average the ascendant moves about 1 degree every 4 minutes; some signs rise faster, some slower. One part of D4 is 7°30′, so a difference of roughly 30 minutes in birth time can change the D4 ascendant. The Moon crosses one part in about 14 hours. In your chart, ePandit shows next to every varga how many minutes of birth-time change would shift its ascendant. Rely on the D4 ascendant only when the birth time is reliable.
How to read it calmly
Read D4 as a second look, not a verdict. Tradition first studies the 4th house and its lord in the main chart (D1), then the running dasha. D4 only helps check whether the same theme shows up here as well. A planet's sign in this varga decides nothing on its own. Make home and property decisions on budget, need and sound advice; a varga is only one traditional pointer.