По мере того как загружался последний слайд, диаграмма становилась чётче.

It means as, while, or more precisely in proportion as. It is used when two processes develop together gradually.

So this sentence is not just saying that two things happened at the same time. It suggests a parallel change:

• the last slide was loading bit by bit
• the diagram was becoming clearer bit by bit

A useful shorter variant is по мере + noun, for example:

По мере загрузки последнего слайда диаграмма становилась чётче.

Here как is part of the fixed conjunction по мере того как. In this expression, you should learn the whole phrase together.

So in this sentence, как does not mean how by itself. The full combination means something like as / in proportion as.

There are two clauses here, and each clause has its own subject:

• последний слайд is the subject of загружался
• диаграмма is the subject of становилась

Both subjects are in the nominative case.

That is why the verbs agree with them:

• слайд is masculine singular, so загружался
• диаграмма is feminine singular, so становилась

The -ся form often makes a verb reflexive, middle, or passive-like.

Compare:

• загружать / загрузить = to load something
• загружаться / загрузиться = to load, to be loading

In tech contexts, загружаться is very common for things like pages, files, apps, slides, and images. Here it means that the slide itself was in the process of loading. English often translates this as was loading or was being loaded, depending on context.

Because the sentence describes ongoing, gradual processes, not single completed events.

• загружался = was loading
• становилась = was becoming

This fits very naturally with по мере того как, since that expression usually focuses on change over time.

If you used perfective verbs, the meaning would shift toward completed results. For example:

Когда загрузился последний слайд, диаграмма стала чётче.

That means more like When the last slide finished loading, the diagram became clearer. It sounds more punctual and result-focused.

Russian does not form the past continuous the way English does. Instead, it relies mainly on aspect and context.

So:

• загружался can mean was loading
• становилась can mean was becoming

The idea of an ongoing process comes from:

• the imperfective aspect
• the context
• the conjunction по мере того как

So even though the Russian past tense is a single form, the meaning can match English continuous tenses.

In the past tense, Russian verbs agree with the subject in gender and number.

• загружался is masculine singular because слайд is masculine
• становилась is feminine singular because диаграмма is feminine

This is normal in Russian past tense. Unlike English, Russian past-tense verbs show gender.

чётче is the comparative form of чёткий, meaning clearer or sharper.

After становиться, Russian very often uses a comparative to show that something is gradually increasing in a quality:

• становиться лучше = become better
• становиться яснее = become clearer
• становиться чётче = become clearer / sharper

If you say становиться чёткой, that means become clear, not specifically become clearer.

You could also say становиться более чёткой, but чётче is shorter and very natural.

Because simple comparative forms in Russian do not decline.

So чётче stays the same no matter what noun it relates to. That can feel unusual to English speakers, especially because it may look a bit like an adverb.

But here it is describing the quality of диаграмма, so the meaning is the diagram was becoming clearer.

Because this is a complex sentence with a subordinate clause.

The subordinate clause comes first:

По мере того как загружался последний слайд,
then the main clause follows:
диаграмма становилась чётче.

So Russian places a comma between the two clauses.

A good practical rule here is to treat по мере того как as one conjunction and put the comma at the clause boundary, not inside that expression.

Yes. Russian word order is flexible.

For example, you could also say:

Диаграмма становилась чётче, по мере того как загружался последний слайд.

That said, the original order is very natural because it introduces the background process first and then gives the main result.

A shorter alternative is:

По мере загрузки последнего слайда диаграмма становилась чётче.

Here it most naturally means last or final in the sequence.

Russian последний can sometimes mean most recent depending on context, but in a slideshow or loading sequence, the obvious meaning is the final slide.