Basically the average wage compared to the cost of living. I'm trying to calculate the buying power of $1.50 a day in 1902, but neither the American or Canadian inflation calculators stretch back that far.
I think "calculate" might be too strong a word here, but you could probably rough it out by researching the cost of the items in the current basket of goods that were available at that time, and compare it to the cost of those items subsequently. The list is contained in this article: https://www.cnbc.com/id/43769766