To balance three sciences, count your recent errors by section, then share your study slots in proportion to the count, keeping at least one slot for every section. The tally replaces the feeling that “physics is the problem” with evidence you can act on.
This page is for students taking Combined Science 0653. Check the scope of your own entry on the Cambridge subject page first, using this route-checking lesson, so that the tally is built from the right syllabus.
Why does revision drift towards the subject you like?
Practising what you are good at feels productive, because answers come out right. Practising a weak area feels slow and a little embarrassing. Without a record, the comfortable section wins almost every session.
A tally puts the drift in plain view. It takes ten minutes and needs only your recent marked practice.
How to build the tally
- Collect your last fifteen to twenty lost marks from marked practice, a topic test or a mixed set from the original mixed-practice builder.
- Write one line per error: the section (biology, chemistry or physics) and the skill that failed, such as “recall”, “rearranging an equation”, “reading a graph” or “explaining in full”.
- Count by section, then count by skill.
- Share your slots: each section gets slots in proportion to its count, with a minimum of one.
- Re-tally every two weeks. The numbers will move as you improve.
Worked example
Amira has six 45-minute slots this week. Her tally from recent practice has 18 errors.
| Section | Errors | Share | Slots |
|---|---|---|---|
| Biology | 3 | 3/18 = one sixth | 1 |
| Chemistry | 5 | 5/18 ≈ 28% | 2 |
| Physics | 10 | 10/18 ≈ 56% | 3 |
The slots add up: 1 + 2 + 3 = 6. Equal slots would have given physics only two, and biology would have taken two slots it does not need.
Now look at the skill column.
Of the 10 physics errors, 6 were rearranging an equation and 2 were graph gradients. So two of Amira’s three physics slots should be spent on equation rearrangement, which also appears in chemistry calculations. The “gap” is partly a maths-handling skill, not a physics one.
The mistake to avoid
The common slip is to stop visiting the strong section. Suppose Amira drops biology completely for a month. Recall in biology fades, and her three errors become eight without her noticing.
The correction: keep one short slot for the strongest section, and use it for mixed questions, not for re-reading notes. The lesson on not letting one strength hide another section covers this in detail.
Check yourself
1. A student’s tally shows biology 4, chemistry 4 and physics 4 errors, with five slots available. How might the slots go?
Show answer
The errors are even, so each section gets one slot (3 slots), and the remaining two can go to the skill that appears most across the twelve errors. Check the skill column before deciding.
2. A tally has biology 2, chemistry 6, physics 4 (12 errors) and six slots. Give the slots.
Show answer
Shares are 2/12, 6/12 and 4/12 of six slots: biology 1, chemistry 3, physics 2. Total 6.
3. Why count errors by skill as well as by section?
Show answer
Because one skill, such as rearranging equations, can cause errors in more than one section. Fixing it once helps everywhere it appears.
Where this leads next
Use the revision plan audit to check the three-science balance of your whole plan, and the mixed practice set to test the result. The study guide for Combined Science shows how the sections fit together.
If the tally keeps showing the same skill even after a fortnight of focused slots, that is a good point to consider one-to-one Combined Science tuition, where a teacher can watch how you work through the question itself.