Based on the fact that only 9.5g of the 13g is used (ie.  3.5g is thrown away), your 9 months drops back to just 6 months for the 120 hour purge timer.
Similarly the 480 hour timer would give you 12 months.

Bruce

Right.  And based on those numbers, each 120 hour purge uses 2.5% of each ink cart.  So translating this to what happens when printing...

If you print frequently, producing many prints each week, the purge cycles won't have much of an effect because by the time you get to a purge cycle, you may have already printed several dozen prints.  Meaning that... the "ink loss" for each purge is small relative to what you are actually printing.

If you print infrequently, let's say one 8x10 per week, you'll get one purge cycle followed by one 8x10 each time.  That works out to 0.25ml from each cart for the purge and .125ml from each cart (on average) for the 8x10 which uses approx. 1ml of total ink (divided by 8 carts).  So printing one 8x10 per week (assuming you print around the same day each week) would result in .375ml of ink being used per cart.  At 10ml of ink per cart before the cart starts complaining it's low, that gives you 26 8x10 prints over 6 months before most (if not all) inks are showing low if you print one 8x10 per week.  In reality, likely less before at least one ink color is showing low because your 8x10 prints will likely use more of some colors and less of others.

If you print infrequently as above (four 8x10 prints per month) but you decide to skip a week and print two 8x10 prints every 2 weeks instead of one per week, you'll get one 120 hour purge cycle and two 8x10 prints each session.  That's 0.25ml of ink per cart for the purge and 0.25ml of ink per cart for the two 8x10 prints (again, a rough average assuming equal distribution of colors in the print) for a total of 0.5ml of ink per cart for the two 8x10 prints.  In this case (printing two 8x10's every 2 weeks instead of one per week), you'll get 40 8x10 prints over about 9 months before each cart is "theoretically low".

In these examples, printing one 8x10 per week gets us about 26 prints out of a set of carts (max) while printing the same number of prints but skipping a week between each print job (two every two weeks) gives us 40 8x10's.  We've gotten 1.5 times the number of 8x10 prints out of a set of carts just by skipping a week between printing sessions.  So where does this leave us?  Does it mean we should all wait and batch up as many prints as possible per job?  If we do that, might it be prudent to print a nozzle check before printing each time and making sure that is clear before proceeding since we are printing infrequently?  If we print when we want with no "schedule" nor do we want to keep track of it, should we still print unclog/purge sheets, particularly if we use third party inks?  I think these are the bottom line questions and since I don't have the answers, I'll leave those answers to the hardware guys like Jose.  

For me, at the moment, I'm still printing unclog sheets every 2 days because I use third party inks and the ink cost is negligible to me.  And I don't know if third party inks tend to clog faster than OEM so being safe seems logical: I don't want to be printing with clogged nozzles because my third party inks have developed a clog that I didn't notice before the next 5 day purge: that could ruin the print head.

Now if I was using OEM inks and wanted to make sure I get the most out of the ink, honestly I might do away with the purge sheets and just try to batch up my prints when possible.  I don't think it's worth "going anal" over personally: I wouldn't keep a tight schedule or worry about when the last purge happened; it's just not worth the effort.  Instead, I'd probably just batch prints when convenient.  For example, if I know I have a print that I want to hang on the wall or show at a club meeting at the end of the month, I might not print it now if I don't intend to hang it right away... or I might wait closer to the end of the month (closer to the club meeting) because by then, I might have a couple more new ones to print and I can print several in one batch.

Suffice it to say, if you really want to get the most (prints) for your ink, just batch print when convenient.  I know I've printed one 13x19 knowing that I'll hang it or frame it when I get time... and knowing that will be some days later.  With this new knowledge about purge cycles, if I was on OEM ink, I would not print piecemeal like that: I'd wait until I have the time to actually do something with the prints and by that time, I might have two or three new ones I also want to print and I can do several in one batch.  Of course, if you use your Pro-100 as a "workhorse" and you are also printing receipts, online payment invoices, and other documents on a regular basis, this all goes out the window because those will "wake up" the printer to print and cause purge cycles in between your photos.  So in a case like that, when printing is unpredictable, I'd be tempted to not worry about the purge cycles at all and just use the printer.  

Mike

An improvement to the above idea:

When your cart gets to a figure of say 70% full, reset it and fill it with the 3.1ml from the previous empty.
That way the ink is not going to hang around for as long, with heaps of empties to store.
The exact refill point needs some experimentation if relying on the print driver advice about ink level.  Weighing will give a good indication.

Bruce

My 120 Hour Purge was due 2 days ago, but I delayed it until today.  I have uploaded the latest spreadsheet.

I think it worth pointing out that the average total ink used for a 120hour purge is now 1.83g.  Down from about 2.0g.  I think that is because the last few purges were for both groups at the same time.  I think I said it previously but keeping the 2 group purges synchronised tends to be more economical.

If you have not already seen it, I started a new thread discussing the ink left in a cart reported as empty by the print driver.  You may want to check that out.

In a previous post I said I did not think the Pro-100 would draw much power in standby mode.  I looked up the specs and it uses 2.1W in standby.  If your power company charged 4 cents per Kwh it would cost about 75 cents a year to leave the printer on permanently in standby.

Bruce

Further thoughts on this.

What difference does it make switching off at mains or leaving  mains on and switching off via front panel.

Is there a battery back up keeping the clock going all the time?

I cannot see anything specific about this in previous posts, but I may have missed it.

At present I leave printer with mains on and use the front switch.

But we have supply via miles of overland wires on posts and suffer frequent short (10 seconds) to longer periods of loss of supply.
also I have a very keen earth leakage circuit breaker, which trips at any mall function, tungsten bulb bowing, the slightest ark on a switch etc.

jeff

I don't believe there is a battery backup.  Although I have never taken the cover off the Pro100 to see.  When you power off via the front panel there is a 0.4W power consumption, compared to the 2.1W when the printer is left in standby mode.

The Pro9000 Service Manual advises: "If the print head has not been capped before power-on" there will be a 3.8g purge (taking 115s).  That is equivalent to a Deep Manual clean.  I am very confident the Pro100 is going to do something very similar.  What it implies is you should always turn off via the front panel before powering off at the mains, otherwise when you next power up it will/could perform a Deep purge (possible exception is case ii below).  The Service Manual makes no comment about what happens if you did power off via the front panel and then turned off at the mains.  You could imply that no purge will occur when you power back on, but there is an element of risk.

I did perform a test of powering off at the mains, after powering off via front panel, back in post #2, but that was before I started weighing carts.  All I can report is that the noises lasted 60s compared to the normal 30s when the mains power is left on.  So something extra is definitely happening, but possibly not a Deep purge, since that would require about 115s.

In an earlier post I also included some comments I received from Canon Support, in answer to my questions.  I did not post any of the first reply I got because I knew some of it was incorrect.  Here is an extract from that reply, which I still would tend to take with some doubt:
"Also, only turn the printer off using the power button.  If you turn the printer by disconnecting the power, either from a wall switch or power strip,  a purge will occur every time you turn it on."

So I believe there are 3 scenarios that need to be considered:
i.   Loss of mains power after a print is complete but prior to printhead being capped (typically 60s after print, 30s of activity).
ii.  Loss of mains power after the printhead has been capped, while in standy mode.
iii. Loss of mains power after power down via front panel switch.

Case i. with definitely result in a deep purge.
Cases ii. and iii. appear to be very similar and may not result in a purge.

So if I am correct, and case i is the only case to be concerned about, then I don't think changing your workflow is going to solve or even improve your situation.

What may be worth looking into are spark quenchers or get a sparky to look at your earth leak circuit breaker.

Bruce

I think you would be doing well to get an answer to this question.  Thinking it through, the most likely source of such a study would be a 3rd Party ink supplier, as they would have the resources and the inclination.
JToolman has a close working relationship with Precision Colors, so maybe worth asking him what he can find out.

Somewhat related to this question, I have seen on another forum a member claiming to have used Precision Colors ink in Pro100 printers until the waste pads became full at 25,000 prints.
The one caveat here is that the printers are obviously in constant use which means the printheads don't get much time for ink to dry.  See this post: https://www.printerknowledge.com/threads/refilling.11808/page-3#post-100646

Bruce

I have updated the spreadsheet for today's 120 hour purge.  I actually stretched the period out to 470 hours.
I did not wish to push it past the 480 hours, as that is expected to invoke a deep purge.
I performed a nozzle check and all is well.

As expected there was no evidence that there is any timer between the 120 hour known purge and the suspected 480 hour purge.

The purged volume of ink was slightly higher that previous 120 hour synchronised group purges.  But I was expecting that because I had removed several ink tanks multiple times to both weight and photograph the actual ink reservoir.  The purpose of these actions was related to investigating the ink monitor(s).  I will post a new thread on that soon.
The ink volumes were very similar to those experienced with exceeding the 60s cart removal timer, so nothing significant.

At this stage I see no value in continuing to update the spreadsheet, as the data is quite stable and I have no desire to exceed the 480 timer.  One thing I did notice is that this time the Yellow cart lost a bit more than the others in-between purges.  Typically this loss is say 0.02g or 0.03g, but this time the yellow lost 0.13g.  I have no explanation other than it may be related to me removing the cart several times.