Imagine this history (imagine that you have not more data) from an zabbix trapper item:

2017-05-22 13:00: 120
2017-05-22 13:05: 100

The graph from 12:00 to 14:00 will show show a stright line from 12:00 to 13:00 on 120. Then I will down to 100, and then it will maintain 100 value until the 14:00

I think the first and the last part should not be present.

I'm uploading an image where you can see the first part. Before the first value it was not data on history.

Thank you very much