running sum

1) The number 'N' of samples to include in the sum can be adjusted with the '+' and '-' buttons. The minimum value of 'N' is 3 and the maximum is 10. 2) Every time the 'SEND NUMBER' button is pressed a new random number (between 1 and 9) is generated and added to the running sum buffer 3) The contents of the running sum buffer are shown on the main activity page. 4) New numbers are added to the running sum buffer until it contains 'N' elements. After that the oldest number is removed before adding the new one so that the length of the running sum buffer never exceeds 'N'. 5) If 'N' is adjusted to be smaller than the number of items in the running sum buffer, the oldest elements are dropped until the running sum buffer contains 'N' elements. 6) The sum of the buffer elements is computed and shown on the main activity page. The sum of an empty buffer is zero.