Ne samo da proveravam napredak, nego i merim puls.

It means not only ..., but also ....

So:

• Ne samo da proveravam napredak = Not only do I check/monitor progress
• nego i merim puls = but I also measure the pulse / measure pulse

This is a very common Serbian pattern for adding a second, stronger, or additional point.

In this construction, da is a normal part of the pattern when a full finite verb follows.

So Serbian often says:

• Ne samo da radim X, nego i radim Y

Here, da does not translate neatly as English that. It is just part of the structure.

You should learn ne samo da ... nego i ... as a set expression.

Because Serbian often leaves subject pronouns out when they are already clear from the verb form.

• proveravam = I check / I am checking
• merim = I measure / I am measuring

The ending of proveravam already shows first person singular, so ja is unnecessary unless you want extra emphasis.

Compare:

• Proveravam napredak. = I check progress.
• Ja proveravam napredak. = I am the one checking progress. / extra emphasis

They are in the present tense.

In Serbian, the present tense can express:

• something happening now
• something habitual or repeated
• something generally true

So this sentence could mean:

• I am not only checking progress, but also measuring pulse
  or
• I not only check progress, but also measure pulse

The exact English translation depends on context.

Proveravati / proveravam is the imperfective verb, which is the normal choice for ongoing, repeated, or habitual actions.

That fits this sentence well, because the speaker is describing an activity or role, not one single completed act.

If you used a perfective verb here, it would usually sound wrong or would change the meaning a lot, because perfective present forms in Serbian often refer to future or completed-type actions rather than an ongoing process.

They are the direct objects of the verbs:

• proveravam napredak = I check progress
• merim puls = I measure pulse / the pulse

That means they are in the accusative case.

For masculine inanimate nouns like napredak and puls, the accusative singular is the same as the nominative singular, so the form does not change.

That is why you see:

• napredak
• puls

and not a visibly different ending.

Both can sometimes be translated as but also, but nego i is especially natural in the pattern after a negative-based first part like ne samo.

So:

• Ne samo da ..., nego i ... = very common and natural
• Ne samo da ..., ali i ... = possible in some contexts, but not the default formula here

In short, for this sentence, nego i is exactly what learners should expect.

Because i means also / too, and its position affects what is being emphasized.

Here:

• nego i merim puls emphasizes the second action: I also measure pulse

If you said:

• nego merim i puls

that would shift the emphasis slightly toward puls, as if you were saying I measure the pulse too.

Both can be grammatical, but they do not focus on exactly the same thing.

Yes, Serbian word order is fairly flexible, but different orders create different emphasis.

The given sentence is very natural:

• Ne samo da proveravam napredak, nego i merim puls.

You may also hear variants like:

• Ne samo da proveravam napredak nego i merim puls.
• Ne proveravam samo napredak, nego merim i puls.

These are related, but the focus shifts a little:

• the original structure emphasizes two full actions
• Ne proveravam samo napredak... can sound more like I’m not just checking progress...

So the version you have is a good standard model.

Not exactly.

Nego often appears after a negative idea and can mean something like:

• but
• rather
• instead

In your sentence, though, it is part of the fixed expression:

• ne samo da ..., nego i ...

So here it is best understood as part of not only ..., but also ..., not as a standalone word with one simple English equivalent.

Yes. Serbian has a few similar ways to express this idea, for example:

• Ne samo da ..., nego i ...
• Ne samo da ..., već i ...

Both can mean not only ..., but also ....

The sentence you were given is fully natural. As a learner, the most useful thing is to recognize ne samo da ..., nego i ... as a common pattern and be able to use it confidently.