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Natural Sciences Tripos


Marking and Classing

The following marking scheme has been approved by the Committee of Management for the Natural Sciences Tripos.


Examiners are nominated by the various Faculties and Departments who contribute to teaching on the Tripos and are formally appointed by the General Board. In each subject, there is a Senior Examiner and other appointed Examiners and Assessors who are responsible for setting the papers and marking the scripts. There is also a Chair of Examiners who, along with the Senior Examiners, assigns classes to candidates and produces the class list and final markbook. The details of processing of marks described below are new from 2022-23. Information about the procedure for earlier years is available here.

The convention in Cambridge is that percentage marks correspond to classes as follows:

First: >=70%

Second: 50-70%

Third: 40-50%

Fail: <40%

In Part IA NST, the Second class is undivided. In later years it is divided into 2.1 (60-70%) and 2.2 (50-60%).

Marks from individual subjects

In each subject, the Examiners produce a raw mark out of 100 for each candidate.

This subject mark is the sum of marks from different components, which may include written papers, written practical examinations, and/or continually assessed work. The maximum available mark in each component will be made clear.

In IA NST, individual subjects are not classed, so there is no particular significance to the 50% and 70% thresholds in subject marks. All individual subjects aim to devise their marking schemes so that the proportion of candidates with raw marks corresponding to the various classes is broadly reasonable. However, the distribution of raw marks does vary between subjects and from year to year, hence a normalisation procedure is used to provide a scaled mark for each subject before they are combined.


Marks in each subject are ranked, and this ranking is used to produce a scaled set of marks with a probability density that follows a normal distribution. The distribution is the same for each subject; see below for how its mean and standard deviation are chosen. In detail: raw marks of less than 40% are not scaled; all other marks are mapped onto a normal distribution with a lowest mark of 40% and a highest mark of 95%. Note that the scaling process does not change the rank order of candidates in a subject.

Combination of marks

Scaled subject marks are averaged to produce an overall percentage mark. In detail, this average is a weighted mean, with a weight of 0.75 given to Mathematics and Mathematical Biology, and a weight of 1 given to all other subjects.

Classes are determined from the overall mark according to the boundaries above. The target class distribution for IA NST is that:

  • 25% of candidates for the Tripos achieve a 1st class
  • 67.5% of candidates for the Tripos achieve a 2nd class
  • 7.5% of candidates for the Tripos achieve a 3rd class or fail.

The mean and standard deviation of the normal distribution applied to the subject marks are set by the Chair of Examiners to achieve these targets.

These parameters will change from year to year depending on the degree of correlation between performances in different subjects. Based on last year’s marks we anticipate that, excluding the small number of candidates with raw marks below 40%, around 5% of scaled subject marks will be in the range 40-50%, and around 30% of scaled subject marks will be above 70%.

Special consideration will be given to candidates close to the 3rd/fail borderline. Normally, a candidate with an average scaled mark of <40% will fail. However, at the discretion of the Examiners, such a candidate may be awarded a Third if their average raw mark is >=40%.


Marks are processed during scaling and combination to full precision, but are reported in the markbook to one decimal place. Reported overall marks are rounded down to one decimal place, so the highest 2nd will typically have a mark of 69.9%.

CamSIS and transcripts

Marks and overall class are released to students on CAMSIS. This information provides the basis for student transcripts. Only scaled marks (total for each subject and overall average mark) are currently available in CAMSIS. Raw marks, including component paper marks, are available in the markbook that is circulated to Colleges, and students may request their own raw marks from their Director of Studies. Raw marks for individual questions are in some subjects communicated directly to students; in other subjects they are communicated to Directors of Studies, to whom students should direct requests if they particularly need this information. Marked exam scripts contain no meaningful additional information and, in accordance with University-wide practice, are not returned to students. Students are encouraged not to focus excessively on the details of mark breakdowns and processing, but rather to concentrate on their learning and performance in future years.

Other Triposes sharing papers with NST

Certain IA NST papers can be taken by students enrolled in other Triposes. The scripts of these students are marked in the same way as those of NST students, but the processing and scaling of these marks is entirely a matter for the Examiners of the other Tripos. The NST Examiners will provide raw marks to the other Tripos, together with whatever information about the NST scaling process the other Examiners request. The targets and resulting scaling described above are based only on the performance and ranking of NST candidates within a given subject.