One is the rati, the deadly Abrus precatorius, commonly known as "coral seeds," "crab's eyes," and so on. They are part of a complex weighing system prescribed by Manu or one of his followers in the Manusmriti (The Law of Manu). This book is called the "Law Book of the Sungas," after a North Indian dynasty that ruled in the second century B.C. It is no doubt built upon even earlier schemes.

The smallest quantity recognized by Manu is a mote seen in a sunbeam. Eight of these are supposed to weigh the same as a small poppy seed. Three small poppy seeds equals one black mustard seed. Three black mustard seeds equal a white mustard seed. Six white mustard seeds are equal to one medium barleycorn (barley grain). Three barleycorns equal one rati. So, one rati weighs (exactly!) 1296 motes in a sunbeam. How is that for precision?

The rati weight was eventually fixed at 1.75 grains. (There are 480 grains in one Troy ounce). Most dealers in precious metals and stones used a "double rati" of 3.5 grains on a day-to-day basis.

In the Middle East, the seed of choice for weighing precious things was the carob seed (Ceraftonia siliqua Linn.). The Latin binomial (the botanical name) indicates that the tree produces siliques (Latin siliqua), that is, pods or husks. It is these pods and their contents that are of interest.

The Arabic name for this tree is kharnub or kharrub, from which we get "carob." We also derive our words "carat" and "karat" from the same root. A "carat" is a weight for gemstones. There are 100 "points" to a carat and five carats to a metric gram. In the US, one carat weighs slightly more at 0.2056 grams -- don't ask me why -- when is this country going metric?

Karat (with a K) refers not to weight but to the fineness of gold. Pure gold is 24 K. Any dilution of the purity (alloying gold with copper or silver to strengthen it) reduces the karat. Thus, 18 K gold has 75% gold; 12 K has 50% gold, and so on. Thus, this system lives on.

Before leaving carob, let's consider the tree's siliques (I just learned this word, so I thought I'd pass it along again). It was carob tree pods the Prodigal Son fed to the pigs (Luke 15:11-32). In one of the most famous of Jesus' parables, the younger son takes his share of his father's money and goes off and squanders it. Then he has to feed pigs and eat what they ate. Depending upon the version of the New Testament you read, this food is called "husks" (K.J.V.), "pods" (R.S.V.; N.E.B.) or the sanitized "food" (Phillips). In any case, carob pods are widely used for animal food in the Middle East and eaten by the very poor.

There is another Biblical connection with this plant, though it is a misconception. John the Baptist, a cousin of Jesus, had become a renowned preacher before Jesus came on the scene. Two gospels (Mark 1:6; Matthew 3:4) describe John as wearing a camel's hair shirt and a leather belt and eating locusts and wild honey.

Now, people did and do eat locusts, but someone along the way decided that John ate the pods of the locust tree (an alternative name for the carob). The pods have since been called "St. John's Bread." But this was some Medieval (?) folly. John ate insects. G.E. Post in 1911 (A Dictionary of the Bible; "husks") went so far as to assert: "There are no carob trees in the wilderness. There can be no doubt as to the possibility of the prodigal son eating the pods." So, there you have it. Evidently, Post made a survey of carob trees in "the wilderness."

The third seed weight is called nakhod in Iran. Don't know it? How about its Arabic name, hummus? (With double letters in Arabic you hold them twice as long; there are even a few words with triple "m"s.) In French it's pois chiche, in Spanish garbanzo (I'll bet you're getting close) and in English, "chickpea."

This humble "poor man's food" is a pulse (an eatable legume, in other words, a bean). It is a staple for many people. It was probably first domesticated in or near the Caucasus -- one has been found in an archaeological site in Turkey dated 5450 B.C. The Aryans apparently brought it to India, which now claims more than 85% of the world's production (Mediterranean lands and Mexico account for most of the rest).

You can stump your dinner guests when having chana masala by asking them what great orator and what city are named for the chick pea. The orator was Marcus Tullius Cicero (106-43 B.C.). His family name is derived from cicer (pulse), comparable to other important Roman families named Lentulus (lentils), Tuburo (roots) and Piso (pea). I had a good friend in Morocco named Mohammed, the most common male name on Earth. He had his friends call him Hammosa or "little chickpea."

Oh, and the city: Homs, Syria.

All very interesting, but what is the chickpea doing on this page? A nakhod, a "chickpea," is the unit of weight for gold and silver in Iran. It is a little less than five grams, so obviously more than one chickpea was the unit of weight.

Now that we have discussed the history, archaeology and etymology of these seeds, a question still nags me. Are they really so consistent in size as to be useful for weights? I don't have any carob seeds, and all my chickpeas are in cans, but I do have some coral seeds from India and Malaysia.

So, I measured them.* A rati is supposed to be 1.75 grains or 0.1134 grams. I have 21 seeds, so I choose five at random, and then eyeballed the rest for the largest and the smallest. The range of weights was from 0.092 to 0.124 grams. The average of the five was 0.103 and of the seven 0.105.

The actual weight varies quite a bit and the average tends to be less than the ideal (only the largest one weighed more than 1.75 grains). This would make no difference in a world in which only the seeds were used as weights, but a goldsmith would get a tad more gold each time when using standard weights against the seeds. He probably wouldn't mind.

• How, you may ask? A friend in charge of the undergraduate laboratories at one of the leading universities in the US took me on a tour of the facilities. (It was first time I actually saw a laser.) Along one wall were a couple dozen fine chemistry scales. They were decades old, but still quite serviceable. I asked him where they were going and he said they were throwing them out because they were converting to digital scales.