Final answer:
For Justin managing an advertising campaign, the daily and weekly sales volume act as a good immediate indicator of the campaign's effectiveness.
Step-by-step explanation:
When Justin is monitoring the advertising campaign, the daily and weekly sales volume would offer him a good indicator of advertising effectiveness.
By analyzing the sales data, Justin can see if the campaign is driving increased sales for the convenience store chain. If there is a noticeable spike in sales during the campaign period, it indicates that the advertising is effective in attracting customers and driving them to make purchases.