public String differenceHours(Registry registry) {
        if (registry.getEndAt() != null) {
            long diff = registry.getEndAt().getTime() - registry.getStartAt().getTime();

            long seconds = diff / 1000 % 60;
            long minutes = diff / (60 * 1000) % 60;
            long hours = diff / (60 * 60 * 1000);
            return hours + "g  " + minutes + "m  " + seconds +"s  ";


        } else {
            return "w trakcie pracy";
        }
    }