Strikkefastheten måles på strikkeprøven.

It is a compound noun, which is very common in Norwegian.

• strikke = knit / knitting
• fasthet = firmness, tightness, solidity

So literally it is something like knitting firmness. In knitting language, the natural English equivalent is usually gauge, and sometimes tension.

Norwegian often combines words into one noun where English would use two or more words.

The ending -en is the definite article attached to the noun, so it means the.

• en strikkefasthet = a gauge
• strikkefastheten = the gauge

This is a basic feature of Norwegian: instead of putting a separate word like the before the noun, you very often add the definiteness to the end of the noun.

Måles is the present passive form of å måle = to measure.

So:

• måler = measures / is measuring
• måles = is measured

English needs two words, is measured, but Norwegian can express that with the -s ending.

Because the focus is on the procedure, not on who does it.

In instructions, manuals, recipes, and knitting patterns, Norwegian often uses passive forms like this:

• Strikkefastheten måles på strikkeprøven.
• literally: The gauge is measured on the swatch.

This is similar to English instructional style, where passive is also common.

An active version could be:

• Man måler strikkefastheten på strikkeprøven.
• You/one measure the gauge on the swatch.

But the passive sounds more neutral and instruction-like.

It is another compound noun:

• strikke = knitting
• prøve = test, sample

So strikkeprøve means a knitting sample, usually called a swatch in English knitting terminology.

And again, -en makes it definite:

• en strikkeprøve = a swatch
• strikkeprøven = the swatch

Here på is the natural Norwegian preposition for something being checked or measured on a physical sample or surface.

So på strikkeprøven means that the gauge is measured on the swatch—that is, by looking at the stitches and rows in that sample.

English may sometimes phrase this a bit differently, such as:

• on the swatch
• from the swatch

But in Norwegian, på is the normal choice here.

Because the sentence is talking about a specific gauge and a specific swatch in context.

In a knitting pattern or instruction, that often makes sense:

• strikkefastheten = the gauge for this project
• strikkeprøven = the swatch you use to check it

If you wanted to make the statement more general, you could say:

• Strikkefasthet måles på en strikkeprøve.

That would mean something like Gauge is measured on a swatch in general.

This is the normal word order for a Norwegian main clause:

• Strikkefastheten = subject
• måles = verb
• på strikkeprøven = prepositional phrase

So it follows the usual subject + verb + other elements pattern.

You could also move the prepositional phrase to the front:

• På strikkeprøven måles strikkefastheten.

That is still correct, but then Norwegian keeps the verb in second position, which is a very important rule in main clauses.