Electronic devices are fine untill they go wrong.
I use 6"x 4" stock cards. Each has it's own plastic sleeve, and they all fit into two 6x4 photo albums. Each card covers a street or small area. The cards are printed with horizontal lines only, I put the columns in myself. Ist column is the house no,
second column the customers name, third column the price of the job. The remainder of the card is filled with narrow columns that make little boxes. I tick the box if they pay, put a zero in if they don't. I then strike through the zero when they do pay.
It is such a simple and infallible system, I have used it since I started, and others cleaners have adopted it when they have seen it.
Always wise to have hard copy in case of major system failure. Dai
Tried posting a copy but won't let me.