One NPC's stats (class feature HP) calculated from a PC's stats (Level) (DnD 5e)

Using an NPC sheet to track a class feature summon's stats, but the HP are based on the summoner's class level and I cant get the HP field to reference another sheet. This vexes me, as all of the other features of the summon which are determined from my stats (save DC, to hit rolls, temp HP granted) work fine. Currently I have [[@{Isri Narnam|level}*5]], tried with several combinations of brackets and syntax.

What sheet?

The one that comes with the paid DnD modules. Sorry, I'm guest GM and I cant figure out how to view it. It looks like "DnD 5e by Roll20"

HP is just called hp, maximum is called hp_max.  @{Isri Naram|hp} should reference the current hp, I believe.

Right. I'm not trying to call Isri's HP though. I'm summoning a creature with HP equal to 5 times Isri's level.

Try using hit dice maximum. 

Sheets are, unfortunately, unable to reference attributes of other sheets when calculating values on the sheet. 1 The reference to the other character's attribute(s) can only be resolved when sent to chat, and the sheet isn't able to react to these rolls. 2  you could make a chat macro that would output what its hp should be and the player or you could then update the summon's token with the proper hp. 1  there are some hacks that can be used in a custom sheet, but they are only usable in some specific circumstances 2  Unless the sheet has a charactermancer coded, but even then it will only react to rolls specified in its code.

Thankyou. I guess I'll just do the math and track them using the health bars. The thought occurs that in a few levels I will have more than one at a time anyway so sharing a health stat is unlikely to work.