Significant figures

Take 0.0450. The zeros at the front only place the decimal point, so they do not count. The 4, the 5 and the last 0 do count. So 0.0450 has three significant figures.

Rounding works the same way. Written to three significant figures, 2.3456 becomes 2.35.

Where does ICSE Physics ask for them?

In practical work. CISCE's ICSE Physics syllabus for the 2028 exam says candidates should use "least count, significant figures and elementary error handling". Least count is the smallest reading an instrument can show. A reading is only as precise as that least count allows.

Do they come up in ICSE Maths?

Yes. Question 2(i) of the 2025 ICSE Maths paper said: "Give your answer correct to three significant figures". CISCE's report on that paper notes rounding errors on this question. Its advice is that rounding be "performed only at the final stage". CISCE's 2027 Maths specimen paper also asks for an answer correct to 3 significant figures.

Why does it matter for marks?

Rounding too early changes the last digits. The final answer can then miss the value the marking scheme expects. The fix is to keep full values in the working and round once, at the end. The same care applies to SI units. Our post on how ICSE Physics numericals are marked shows the working CISCE expects.

About the author

Mohit Sardana

Chief Architect

An engineer (B.Tech, Computer Science) with over 20 years of preparing students for entrance exams, including as Dean at FIITJEE and Vice-President at Aakash. He is the chief architect of the TRUpreBoards evaluation engine.

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