How to compute plot values from tag historian

For example i have a tag that ranges between 0 and 10. For some reason i want to divide this by two so it only goes to 5. i want to do this without imply hacking the Y-axis.

abother example, i want to create a ribbon chart, where anything above 4 shows as 1, and everything else as zero. again withoutdoing dodgy stuff to Y axit