Look for hard raw mango with dark green skin. Signs of yellow means the mango is ripening and it will be difficult to achieve the sweet and sour taste.The amount of sugar should equal the weight of unskinned mango. Unless you buy the indian pickling mango(rajapuri) you will most likely need 20 to 30 % less sugar. I have been using the south American mangoes marketed for consumption as a fruit and these tend to be sweet. Hence I use almost 40% less sugar. The creamier the flesh, the more sour the mango. Less sugar will mean the syrup will be slower to develop.I must acknowledge that this is Lalitaba's recipe. Like with most recipes, I can still not emulate her chundo!