#!/bin/bash
old=-1
while read line; do
	date="${line%	*}"
	dl="${line#*	}"
	if [ "$old" -gt -1 ]; then
		if [ "$dl" -lt "$old" ]; then
			delta="$dl"
		else
			delta=$(( $dl - $old ))
		fi
		echo "$date	$delta"
	fi
	old="$dl"
done