A balance has a weight of 1 gram, 2 gram, 4 gram and 8 gram each. How many different masses can be weighed on the balance with these 4 weights?
一架天平有1克、2克、4克和8克的砝码各一个，用这4个砝码在天平上一共可以称出多少种不同的质量．
<gadget id="calculator">1 + 2 + 4 + 8</gadget>
<output>15</output>

<result>15</result>