If all you want to do is check your current to the boards and have a quick reference for the adjustment screw on the A driver, there's a simple method I use that's at least 98% accurate.
(EDIT: Ensure the Vo adjustment is at maximum volts - use only the Io current adjustment for this method - this will ensure the driver is in constant current mode.)
If you don't want to wire a permanent meter in, get yourself a cheap wall meter and multimeter. Connect the multimeter using wagos to measure the current, then note what the total wattage is at the wall meter. Do it again as you increase the current in increments and note down the wattages on a piece of paper.
You'll end up with a reference chart that tells you the current to the boards for a particular wall meter reading.
After you've done that, it's a simple task to adjust the A driver to whatever wall meter reading you know corresponds with whatever current you need - no need to hook up your multimeter again. You can then use your multimeter to test the voltage at whatever current you have set so that you can work out how much power the driver is using. (Multiply voltage by current to get board watts, then have a look at the wall meter to see how many watts are being used by the driver.)
Accuracy: as the boards (LEDs) heat up, the voltage reading for the same current will fall bit-by-bit until the LEDs - and voltage - stablise. You'll see this at the wall meter. When you turn the boards on and set the current, you will note that the wall meter reading will start to fall bit-by-bit until the boards have fully warmed up. Once the temperature of the boards has stabilised, the wall meter reading will stabilise.
So, how to ensure accuracy?
Well, the relationship between LED voltage and current will change as LED temperature changes. A number of things can affect LED temperature, such as ambient temperature and heatsinking - such as having a fan blowing on the boards etc.
So the above method will never be 100% accurate, but it will be close enough if you do one of two things. You can either wait for the boards to stablise when you take the readings - you'll know they have stabilised, because the wall meter wattage will not change (or change very little) - or you can take all your readings when cold (this is faster, but slightly less accurate)
As long as you are consistent, you'll be fine. And honestly, the difference in voltage between 25C and 85C on those LM301B LEDs is only 3%, so using this method means a maximum inaccuracy of 3%, but usually only 1-2%. That is within the tolerance of some multimeters and wall meters.
Want an even simpler - but slightly less accurate (and still good enough) - solution?
Forget the multimeter. Get a wall meter, plug it in. Use the HLG reference chart here:
https://horticulturelightinggroup.com/collections/quantum-boards/products/qb288-v2-quantum-board
That 320H-48A Mean Well driver of yours is 91-92% efficient at almost all loads (Page 6):
https://www.meanwell.com/webapp/product/search.aspx?prod=HLG-320H
Whatever the wall meter says, multiply that by 0.92. That will tell you the wattage at the boards. Use the HLG reference sheet to see how many volts and amps the boards draw at the corresponding wattage.
For example, the wall meter says 290W. Multiply that by 0.92 = 267W. Divide by 4 boards = 66.7W per board. HLG reference sheet says 66.78W is 1400mA at 47.7V at each board.
This method will never be 100% accurate, but it will be close enough and is very cheap and easy to use.
But if you're happy to wire in a permanent meter like the ones others in this thread have posted, that is obviously your best solution.
![0611191341a[1].jpg](/data/attachments/3450/3450031-44c4616b980caf08c6eb8afd320ade39.jpg)
Do you think this would be a good option? 
