Well yeah that's obvious lol, I just have to dig it out to see.
However what I'm wondering how to test it to see if it's actually accurate.
it's only a voltmeter, you'll be using, so you can just test it on a range of applications. wall socket, car battery, remote battery, 2 remote batteries in series, car alternator (turn car on and put leads on battery), etc.
if all seems to check out and looks ok, the low end of the meter calibration shouldn't be too iffy. basically... for the most part, when they're off, they're off noticeably or at least within their given range (+/- _._ %). it's likely you can look up your model# and find the %accuracy range.
the absolute accuracy of the sensor is already +/-5%. even a $20 multimeter commonly has a rated accuracy of ~0.5% @ 100 uV resolution... if it's capable of such a resolution. there's a multimeter going for $19.99 on amazon right now labeled as "L:AC/DC Digital MultiTesters Multimeter Hand Tool Meter"
. if you do a search for that and check out the stats, you'll see what i'm talking about.
a better voltmeter isn't going to amount to an overwhelming increase in accuracy. the type of light you're reading and how you account for that would be much more beneficial considering the ~10% apparent difference between sun and electrical lighting calibration between units. 5% and 10% discrepancies are massive in comparison to any digital multimeter that i'm aware of.
example: assuming the light you're testing results in perfect measurements per your units calibration...
say your reading comes out to 20 umols (4mV exactly)
+/-5% for the sensor = 19 - 21 umols (3.8mV - 4.2mV)
+/-0.5% for the cheapy voltmeter = 18.905 - 21.105 umols (3.708mV - 4.221mV)
as far as the security doohickey, i'd be more interested to see how they treat the U.S. market and how the product fares/works. it seems to be more of a continual use item which would significantly increase degradation in comparison to a unit stored in a cool, dark place until it's needed for use. this would incur an increase of ownership cost that seems to me would negate the initial savings in short order. i'd be curious to its usefulness when utilized as an intermittent use device. turn it on, gather my data, turn it off and put it away until next use, etc.. i notice it mentions hourly data recording. i'd be curious if that's an hours worth of data or a single point recorded every hour. i see no display, either. that seems like a hassle when attempting to gather data sets for different regions of the tank. i'd hate to e forced to go back and forth from my tank to my pc to keep uploading data from each zone. seems a recipe for disaster.