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Math Recall shows you numbers, hides them, and then asks you to compute with them. You are holding values and operating on values you cannot see, which is a genuinely harder task than either memorising numbers or doing arithmetic. It is the closest thing here to mental arithmetic as it actually happens in life.
Numbers are shown for a short period.
They disappear from the screen.
An arithmetic question about them appears.
Answer from memory — nothing is redisplayed.
Rounds add numbers and more complex operations.
Working memory under processing load — the combination that laboratory 'complex span' tasks are built around. Holding while computing is measurably harder than holding alone. Another memory game to try next: Memory Blitz.
Rehearse the numbers as a rhythm rather than as a list. Rhythm survives the arithmetic step better.
Do not start calculating before you know the question. Precomputing the wrong thing wastes the memory.
Chunk pairs that are easy to combine, so you hold two values instead of four.
If you lose one number, answer with the rest rather than abandoning. Partial credit beats none.
Because holding and computing compete for the same limited capacity. That interference is exactly what complex span tasks are designed to measure.
You can, and then the task measures nothing. The whole point is what happens without notes.
Digit Span asks you to hold and reproduce. This asks you to hold and operate, which is the harder half.
Combine as you go where the question allows it — holding one running total beats holding four separate numbers.