History
While you are using the Standard Calculator, the history shows only calculations performed in the Standard Calculator.
Use expression. Swipe a calculation to the left, tap More, then tap "Use Expression". MathX tries to insert the result at the current cursor position if possible. Otherwise, it erases the current calculation.
Use result. Tap a calculation to use its result, or swipe a calculation to the left, tap More, then tap "Use Result". MathX tries to insert the result at the current cursor position if possible. Otherwise, it erases the current calculation.
Delete calculation from your history. Swipe the calculation to the left, then tap Delete.