Using pencil would be highly frowned upon I would think (other than at the bottom for your totals). Using an electronic log is great, but I would ALWAYS keep a paper log also. I keep my first logbook in the fireproof safe, my current paper logbook is ALWAYS current also, in addition, my electronic logbook is always current, PLUS, a current backup copy on a thumb-drive in the fireproof safe, another copy on an external hard drive and a backup of the logbook on my main drive. Could you imagine trying to recreate decades of flying??