def human_estimate(self, upgrades):
        val = self.estimate(upgrades)
        if val < 60:
            return "less than 1 minute"
        elif val < 300:
            return "less than 5 minutes"
        elif val < 600:
            return "less than 10 minutes"
        elif val < 1800:
            return "less than 30 minutes"
        elif val < 3600:
            return "less than 1 hour"
        elif val < 3 * 3600:
            return "less than 3 hours"
        elif val < 6 * 3600:
            return "less than 6 hours"
        elif val < 12 * 3600:
            return "less than 12 hours"
        elif val < 86400:
            return "less than 1 day"
        else:
            return "more than 1 day"