The usual HRV app flow: data → algorithm → verdict → user. HRVSpark reverses it: data → user → intuition. Raw SDNN sparklines and gauges on your Apple Watch face, across four time windows. Complication-first — always visible, never buried in an app. Works alongside analysis suites like Athlytic or HRV4Training, or stands alone as your only HRV tool. $2.99 one-time. No subscription. No account.