bang 

In left inlet: Using the number most recently received in the left inlet, histo reports out the right outlet how many times that number has been received, and sends the number itself out the left outlet. If no number has been previously received in the left inlet, 0 is sent out both outlets. 
int 
countednumbers [int]

In left inlet: histo keeps count of how many times it has received a number between 0 and 127 in the left inlet. When a number is received, histo includes it in the count, sends the number of times that number has been received out the right outlet, and passes the number itself out the left outlet. Numbers outside the range 0127 are ignored. 
(inlet1) 
discountednumbers [int]

In right inlet: Has the same effect as a number in the left inlet, except that the number is not counted by histo. 
clear 

Erases the memory of histo, to begin a new histogram. 