Like many an astrologer when posed with that question, I've twitched perceptibly, wondered if I really understand it myself, and if so can I explain it to the satisfaction of the querent.
Most Western astrologers use what is called the Tropical Zodiac of the twelve signs.
Hindu astrologers on the other hand use the Sidereal Zodiac of the fixed stars based on the positions of the actual constellations from which the signs derive their names. That difference of 70 years sounds a lot but remember it only equates to about 1 degree of arc. At the present time because of precession the Tropical Zodiac and the Sidereal Zodiac are about 24 degrees apart. Hindu astrology also divides its zodiac into twelve equal segments but these refer to the position of the actual constellations - almost, because none of the twelve zodiacal constellations is exactly thirty degrees of arc, some are a little less, one or two a great deal more. So like the western system it is still only a hypothetical model to work from.