Fill multiplier field, confirm Add button disabled

app/helpers/application_helper.rb

@@ -132,4 +132,10 @@ module ApplicationHelper
   def disabled_attributes(disabled)
     disabled ? {disabled: true, aria: {disabled: true}, tabindex: -1} : {}
   end
+
+  def number_attributes(type)
+    step = BigDecimal(10).power(-type.scale)
+    max = BigDecimal(10).power(type.precision - type.scale) - step
+    {min: -max, max: max, step: step}
+  end
 end

app/views/units/_form.html.erb

@@ -14,8 +14,8 @@
       <% unless @unit.base.nil? %>
         <%= form.hidden_field :base_id, form: :unit_form %>
         <%= form.number_field :multiplier, form: :unit_form, required: true,
-          step: BigDecimal(10).power(-@unit.class.type_for_attribute(:multiplier).scale),
-          size: 10, autocomplete: "off" %>
+          size: 10, autocomplete: "off",
+          **number_attributes(@unit.class.type_for_attribute(:multiplier)) %>
       <% end %>
     </td>