Usomaji wa mita si usomaji halisi wa mita.

Usomaji is a noun meaning reading or the act/result of reading.

It is built from the verb kusoma = to read, with noun-forming morphology:

• ku-soma = to read
• u-som-aj-i = reading

So in this sentence, usomaji is not a verb. It is a noun.

Wa is the connective word often translated as of.

So:

• usomaji wa mita = reading of a meter / meter reading

In Swahili, this of-link changes form depending on the noun class of the first noun. Here, usomaji takes wa, so you get usomaji wa mita.

Because the connective agrees with usomaji, not with mita.

That is an important Swahili pattern:

• the linker agrees with the noun that comes before it
• not the noun that comes after it

So:

• usomaji wa mita = correct

Even though mita belongs to a different noun class, that does not control the form of the linker here.

Si is the negative copula here. It means is not / are not in sentences where one noun phrase is being identified as another.

So the pattern is:

• X ni Y = X is Y
• X si Y = X is not Y

In your sentence:

• Usomaji wa mita si usomaji halisi wa mita
• A meter reading is not an actual/real meter reading (or similar, depending on the context already given)

So si is doing the job of is not.

In simple identification sentences, Swahili usually does not need a full verb meaning to be.

Instead, it often uses:

• ni = is/are
• si = is not/are not

So Swahili commonly says:

• Yeye ni mwalimu = He/she is a teacher
• Yeye si mwalimu = He/she is not a teacher

Your sentence follows that same pattern.

Because adjectives normally come after the noun in Swahili.

So:

• usomaji halisi = real/actual reading

This is the normal order:

• noun + adjective

Also, halisi is one of those adjectives that often stays the same in form instead of changing to match noun class.

It is repeated because the second half is a full noun phrase again:

• usomaji halisi wa mita = an actual/real meter reading

So the sentence is comparing:

• usomaji wa mita with
• usomaji halisi wa mita

Repeating wa mita makes the second phrase complete and precise.

If you removed it, the sentence structure would change, and the meaning could shift.

Yes, that is possible, but it would not mean exactly the same thing.

• Usomaji wa mita si halisi = The meter reading is not real/accurate/genuine
• Usomaji wa mita si usomaji halisi wa mita = The meter reading is not an actual/real meter reading

The given sentence is more explicit because it contrasts one noun phrase with another noun phrase.

Often mita has the same form in both singular and plural, especially as a loanword.

That means:

• mita moja = one meter
• mita mbili = two meters

So the exact number is usually understood from context, or from a number word if one is present.

In this sentence, the grammar does not force a singular/plural distinction in the English way.

Because Swahili does not normally use articles like English a, an, or the.

So a phrase like usomaji wa mita can mean:

• a meter reading
• the meter reading
• sometimes just meter reading

The exact sense depends on context.

Here it is functioning like an abstract or action noun: reading.

Swahili often uses nouns like this to talk about:

• an action
• a process
• a result

So usomaji can refer to the act of reading or a reading depending on context. In this sentence, it works well as a technical noun, similar to English reading in meter reading.

The structure is:

• usomaji wa mita = subject noun phrase
• si = negative copula
• usomaji halisi wa mita = complement noun phrase

So, very roughly:

[Noun phrase] + si + [Noun phrase]

That is a very common and useful Swahili pattern for saying that one thing is not another thing.