Halve lime pole to pole, cut off ends, then slice into 4 or 8 segments, as per Caipirinha. Muddle lime and sugar in old-fashioned glass vigorously, to combine and release flavours from zest. Stir in rum and cracked ice.
A very good alternative is to use Plantation Fiji.
The key to this drink is the palm sugar. Look for the rich, fudge-like, more expensive stuff in a pot with a lid in Thai or oriental food stores. I prefer the Maesri brand. With larger or more bitter limes, 2 or 3 tsp sugar may be needed.
I use a Tap-icer for the cracked ice; crushed ice tends to wash out drink.
A Caipirinha-style navy grog.