If you want an easy rule for the 21st century for pure gold, to determine nominal value in De-Saussurian terms, you could see 3 gram of pure gold as being 4 Spesmiloj. (strictly more like 4.09).

For example, that would make a ducat nominally 4.601 Sm (which is close to the 4.706 Sm, more strictly calculated). So about a 2.25% error - not bad

I realise, that unfortunately there is no easy rule other than the one you've said: 0,8 g of gold (of fineness 916) equals to 1 spesmilo. And I took that 916 from the Wikipedia article about fineness rather than from 22/24. I can well imagine people being sensitive against any non-strict calculations, when it comes to gold or money. So you/we should pick one and stick to it. I prefer the one above and I've already used it in a business proposal

Metsis I wasn't suggesting that we abandon the de-Saussuran difinon. Merely suggesting a quick method for approximately converting into nominal Spesmila value any gold item whose fineness and weight in grams is known.

For example, suppose you have a ring hall-marked as 9 carat gold and the ring weighs w grams.

What is that worth in Spesmiloj? Well you could work out the contained gold and divide that by .7333 (.8 x 22/24).

On the other hand, if you don't have a calculator to hand, you could quickly calculate the Spesmilo value with my suggested approximation (3 gram pure gold = 4 Spesmiloj).

Thus w x (9/24) x (4/3) - which simplifies to w x 3/6 or w/2.

So a 2 gram ring in 9 carat gold is roughly and nominally 1 Spesmilo.

Of course how much you should pay for a Spesmilo in dollars, pounds, euro's rubles etc is another question and the subject of my proposal in another thread.