Need Details on Zoya Zakat Calculator App

Can someone explain to me how the zoya zakat app calculates the zakat? I tried using the calculator and did it myself using the calculation provided and arrived at very different values. I used SPUS as an example (current net assets of 1.1B and outstanding shares of 27.65M). I got a value of approximately $500 for 500 shares of SPUS vs the calculator which had $51.88.

If someone could share some insights or correct my understanding, I would appreciate it.

My calculation was:
1.1B x 500 / 27.65M x 0.025 = $497.28