Penny and Bill tracking legend on an electronic device
I believe the answer is:
keypad
'an electronic device' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'penny and bill tracking legend' is the wordplay.
'penny' becomes 'p'.
'and' means one lot of letters go next to another.
'bill' becomes 'ad' (advertisement stuck on wall).
'tracking' means one lot of letters go next to another (track can mean to follow or go after).
'legend' becomes 'key' (legend can mean a key on a map or diagram).
'p' put next to 'ad' is 'pad'.
'pad' after 'key' is 'KEYPAD'.
'on' acts as a link.
Can you help me to learn more?
(Other definitions for keypad that I've seen before include "Small unit with push buttons" , "Device for data entry" , "What might help you calculate" , "where characters get depressed" , "Feature used to operate a portable electronic device" .)