3. The method of claim 1 wherein the first number is a weighted combination of a plurality of the views of the document wherein one or more of the views is weighted using a respective weight based at least in part on a respective viewing duration of the document.
3. The method of claim 1 wherein the first number is a weighted combination of a plurality of the views of the document wherein one or more of the views is weighted using a respective weight based at least in part on a respective viewing duration of the document. 6. The method of claim 3 wherein the weight is determined using a discontinuous function of viewing length.