because different calculator models have different input manner & diff button placements. if you're not familiar with a certain calc model, you waste time during the using of the calculator in the time-tight test. (and it's unfair if some candidates heng heng very familiar with the provided calculator while the remaining suay ones struggle with the learning curve during the test itself. how stressful pls) and of course, i'm only referring to Scientific calculators (those permitted for GCE O-levels kind).

i just find it weird that mindef's test doesn't involve math and calculation. most Psychometric tests have numerical component.