Now we use this system - it works well for us.
A 2 part invoice where the electrician writes in detail job, location, description of work, labor, material, total price, notes, etc.
Then has the customer sign the invoice, gives them a copy, collects a check, turns in to office at end of day the 2nd copy with check and material slip from supply house if has one, and any notes to follow up.
Then it goes into the computer system in the office.
A lot of larger jobs are billed from our office anyway, so the guy in the truck also has a daily log where he records times, addresses, notes, materals, etc which he turns in to office as well. He doesn't need a computer for that anyway.