Learn German: Der Meister mischt präzise zehn Milligramm Rose in das Öl. - The master precisely mixes ten milligrams of rose into the oil.

This is the zero-plural rule for measurements! Masculine and neuter nouns used for weights and measures (like das Milligramm, das Kilo, or der Liter) do not get a plural ending when they follow a number. They stay exactly the same as their singular form.

How come there is no word for 'of' between Milligramm and Rose?

In English we say 'ten milligrams of rose', but German usually drops the preposition. When giving a quantity or measurement, the substance being measured simply follows directly after the unit.

Why does the sentence use the accusative in das Öl instead of the dative in dem Öl?

The preposition in is a two-way preposition. Because the action describes movement into a new place (mixing the rose into the oil), it takes the accusative case to show direction. If the rose were already resting inside the oil, you would use the dative (in dem Öl) to show location.

Why doesn't präzise take an adjective ending here?

In this sentence, präzise is used as an adverb describing how the master mixes, rather than describing a noun. German adverbs never take grammatical endings; they just use the base dictionary form of the word.