In Game of Thrones S07E01, someone weighs a body part (not being specific to avoid spoilers)-- and finds that it weighs 147 (or something). It always bothers me when people specify unit-less measurements. 147 what? Stones? Kilograms? Pounds? Is there a special block of metal that sets this standard?
ETA: It appears the Archmaester Ebrose was documenting the weights as "penny" in the scene for the basis of the question.
Based on the evidence below, I am fairly certain this would refer to a pennyweight. Whether or not this actually makes sense though is another question.
And now back to your regularly scheduled answer...
We do know George based his world on medieval Europe. We see throughout the books that both pounds and stones are used by many characters from various parts of the world (a small sample is given below). These are most likely the base units, however we do not see any smaller units of measure.
Ned uses stones:
Since the night they had stood side by side in Greyjoy's fallen stronghold, where Robert had accepted the rebel lord's surrender and Ned had taken his son Theon as hostage and ward, the king had gained at least eight stone. - A Game of Thrones - Eddard I
Jon uses pounds and stones:
By the look of him, he must have weighed twenty stone. - A Game of Thrones - Jon IV
Rast had two years and forty pounds on him. A Game of Thrones - Jon IV
Tyrion makes reference to pounds and stones as well:
He needed help to mount; he felt as though he weighed a thousand stone. - A Game of Thrones - Tyrion VIII
The boy's clothes his host had dressed him in made him feel like ten pounds of sausage in a five-pound skin. - A Dance with Dragons - Tyrion II
Traders also seem to use pounds in the deals:
Not to mention cloves and nutmeg, and a pound of saffron. - A Dance with Dragons - Davos I
Daenerys uses stones:
The old man had the look of Westeros about him, and the brown-skinned one must weigh twenty stone. - A Clash of Kings - Daenerys V
Ounces are only used once, and a bit of a colloquial way:
Balon Greyjoy had always been thin, but now he looked as though the gods had put him in a cauldron and boiled every spare ounce of flesh from his bones, until nothing remained but hair and skin. - A Clash of Kings - Theon I
George has been known to keep things vague so as fans have a harder time picking up on his mistake. I would suggest that the show is following suit... don't give units because first, we don't know, and second, we don't want to be "wrong".
There is no explanation as to what their weights and measures are based on in The Game of Thrones
throughout the show and books various weights are mentioned which includes pounds so the easiest answer would be to assume they meant 147 grams since grams are a sub unit of pounds and 147 of anything else would be way to much for any body part
Edit: Grains and pennyweights are actually the sub units of ounces and pounds and 147 of either could still work
As George RR Martin quoted the planet of Game of Thrones is slightly larger than our earth. Units of mass would not be comparable.
But I must admit: Probably the show makers and GRRM have not thought about this.