type = models.CharField(choices=TYPES, max_length=255)
    other = models.CharField(max_length=255, blank=True)
    sub_type = models.CharField(choices=SUB_TYPES, max_length=255)
    power_supply = models.CharField(choices=POWER_SUPPLIES, max_length=255, blank=True)
    manufacturer = models.CharField(choices=MANUFACTURERS, max_length=255)
    manufacturer_contact_name = models.CharField(max_length=15, blank=True)
    manufacturer_contact_phone = models.CharField(validators=[phone_regex], max_length=17, blank=True)
    manufacturer_contact_email = models.EmailField(verbose_name=_('Email address'), max_length=255, blank=True)
    manufacturer_product_type = models.CharField(choices=MANUFACTURER_PRODUCT_TYPES, max_length=255)
    name = models.CharField(max_length=128)
    description = models.TextField(blank=True)
    location = models.TextField(blank=True)
    first_day_of_operation = models.DateField()
    status = models.CharField(choices=STATUSES, max_length=255)
    last_status_change = models.DateTimeField(auto_now=True)
    last_service_performed = models.DateField(blank=True)
    last_service_provider = models.ForeignKey(ServiceProvider, on_delete=models.SET_NULL, blank=True, null=True,
                                              related_name='last_provider')
    runtime = models.CharField(validators=[runtime_regex], max_length=6, blank=True)
    remarks = models.TextField(blank=True)
    asset_owner = models.ForeignKey(AssetOwner, on_delete=models.SET_NULL, null=True)
    service_provider = models.ForeignKey(ServiceProvider, on_delete=models.SET_NULL, blank=True, null=True,
                                         related_name='current_provider')
    document_1 = models.ForeignKey(Document, on_delete=models.SET_NULL, null=True, related_name='document_1', blank=True)
    document_2 = models.ForeignKey(Document, on_delete=models.SET_NULL, null=True, related_name='document_2', blank=True)
    document_3 = models.ForeignKey(Document, on_delete=models.SET_NULL, null=True, related_name='document_3', blank=True)
    document_4 = models.ForeignKey(Document, on_delete=models.SET_NULL, null=True, related_name='document_4', blank=True)