Since I started building apps back in 2007, I’ve been keeping a list. This is a list of technical pitfalls to avoid when building a new app. Here are a few:

• timezones

• daylight saving time

• shoe sizes

This list has grown over the years and I thought I was in the clear with Cushion until I discovered I needed multiple currencies. Currency! Normally, this wouldn’t be a problem, as it’s just a matter of formatting, but I quickly realized a much bigger problem—combining currencies.

Looking ahead to integration with other services, I noticed that Harvest allows varying currencies per client and per invoice. Freshbooks only varies per client, but allows switching a client’s default currency for current and future invoices. With this in mind, along with Cushion’s interface, I’ll need to combine currencies both visually and in table form.

The table side of combining currencies is the easier of the two. Instead of trying to calculate a total based on the exchange rate of whenever you received a specific invoice, you can simply show multiple totals per currency. It won’t look as good as a single total, but it’s a much better route than driving down the road to insanity via exchange rates.

On the visual side, specifically the budget timeline, I’m in a bit of a pickle. These timelines are based on a financial goal the user sets in the beginning, which is of a single currency. This means that if I want to visualize a variety of currencies, I’ll need a goal per currency, which is not going to happen.

I have a few ideas of how to get around this, but I’m getting ahead of myself. As a first step, I just need the ability to change the default currency per user. This is an easy one, so I’m happy to say it’s already done. I found a Ruby gem, called Money, that provides a thorough list of currencies, along with their symbols, symbol positions, thousand separator, and decimal separator. On the front-end, I can still use Accounting.js—all I need to do is provide the currency settings from the backend.