Where would the modern world be without scientific instrumentation? The voltmeter, the thermometer, the Geiger radiation counter, the Lady Margaret cat counter... All essential in everyday life.
Everywhere you look, it is important to be able to measure things. Take an ordinary domestic fax machine, such as you probably have in your kitchen or bathroom. How viscous is it? Well, what a ridiculous question, you might think; it would never occur to you that this could be an issue.
When the fax machine was invented by Heron of Alexandria in 42 AD, though, it was a very different story. Peoples' fingers would go through the keypads all the time when dialing numbers (of which there were three, at the time) and the machines would get stuck to things. The invention of the Smith-Smythe-Smith fax machine viscouometer in 1932 changed all this, though, by allowing economical detection of problem machines on the production line, and helped push the fax machine into common use, though the really great advance in fax machine acceptability came when the solid, as opposed to liquid, fax machine was introduced.
But, what of this holimeter? Well, it is apparently the case that one can dilute holy water to up to a half without impairing its holiness; any further and it becomes non-holy water. This leads to an obvious issue; how do you know that the holy water you're getting is actually holy?
Currently, the accepted method for checking this is to throw a sample on your local homosexual, harlot or fat person. If they burst into flames, then the water is clearly holy. If they simply melt, then they are a witch, and so the test is inconclusive. Remember that with the recent invention of the heavy-lift broom stick, even fat people can be witches! Now, this is all well and good, but as people become more and more concerned about consumer issues, more people will want to check that the water they're getting is really holy, and demand for test subjects may outstrip supply. In addition, the fat people are beginning to resist.
The old method also leaves questions unanswered. Does the holiness of the water go straight from holy to not holy, or are there degrees of holiness? Research theologians have been trying to determine this for millennia, but the most recent studies, typically involving the participation of an escort agency and large quantities of asbestos, are still inconclusive.
So, the holimeter. Take an ordinary domestic 7.29 volt battery, and attach one terminal to a piece of the True Cross. Connect a consecrated (transubstantiated, gluten-free) communion wafer in parallel with the True Cross, and place a small quantity of the tears of a miraculous weeping statue in a beaker, wired in series to the previously-mentioned apparatus. Place the sample to be tested in a Bessemer plate connected to the tears and the other terminal of the battery, and wire a galvanometer in parallel to it. The device may be calibrated using ordinary water, goat's blood from a Satanic rite, and Pope urine. The latter is available from all good pharmacies.
And there you have it! Cheap, efficient, accurate holy water measurement. But that's not all! Think of the other applications! Concerned that your bishop may not be a real bishop? Simply dissolve in acid and check! Fun for all the family.
(This is exactly why I shouldn't use the Internet while tired.)