I own a TNC and a Hanger 9 Mini Tach, which are about $120 and $28, respectively. I think they're very close to equal in performance. You can set either on the ground (grass or pavement) about 18'' ahead of the plane, and get a good reading. None of the others will do that. I'd suggest the Hanger 9 Mini Tach, of course. I even bounced mine off the concrete last weekend, and it still worked fine. I don't think my TNC would have survived. It had never been dropped, but still had the DRO plate go wonky. Some glue fixed it, tho.  Hope this helps!  Steve

     http://www.hangar-9.com/Products/FieldEquipment.aspx?CatId=APE 

Don't bother with the Tower Hobbies Digital Mini Tach.  I've bought at least 4 of these.  They work well for awhile, but all of them died over the winter.
Thunder Tiger makes a decent tach, but it only reads 4 digits, so 15,900 shows up as 159.  It also is very fussy about what it sees.  Has to be right on top of the prop and up sun of  it.

Yes, batteries are  a secondary issue here. My first TOWER HOBBIES DIGITAL MINI-TACH uses about $20.00 worth of hearing aid batteries. And it has no facility for turning itself off after a certain period of time. So, imagine what happens when I put it down and forget to turn it off!!!

I've since discovered I can break down a $3.50 Duracell battery into its individual cells and use them...

Ward

I also use the hanger 9 tach, but i wouldn't suggest setting it in on the ground in front of a running engine ! it doesn't weigh much and i would think it would be sucked into the prop!!!
 that would be Bad,very Bad
Dave jr.

Yeah I remember Vibra Tachs, they also made a biger industrial version. I ran a concrete paver that had multiple large cylinder style hydraulic vibrators in the hopper to help move the mix through.
We used a vibra-tach to try and match up the freq on the entire set so the mud was vibrated consistantly across the width of the slab, sometime 24' with a vibrator every 18".
Good times standing in a metal box full of wet concrete with a dozen big vibrators howling around you while you try and get a reading from the scale on a buzzing blur of concrete covered tach. If we matched them up to within 1/4 range of the scale on the tach we were doing good!
Eventually drooped it in the mix and it disappered - it's still somewhere in U.S. Hwy 2 Westbound in Grand Forks ND.

Sheesh, now you tell me,  My Globee did that too, I thought the batteries were dead when it did that. I bought a tower to replace it, well I guess I will try it again now, probably keep it in my ice chest with my lunch!

The incandescent lightbulb also works for calibration check, as long as it is powered by 60 cycle electrical source. This originally was used as the calibration for the Heathkit "Thumb Tach". I believe some countries use 50 cycles, so I guess it would read 3,000 rpm there?

I noticed this weekend that my Hanger 9 tacho shut down after "awhile"...15 sec or 30 sec or whatever. It's the thought that counts! Anybody know what watch battery it takes, please post! "Gotta have spares!"  Steve

...All but two tachs I have tested are well within reasonable accuracy... The second was a TNC that was off by about 500 at 15,000 rpm. 

Larry, any idea if that was one of Tony C.'s original tachs or the "new and improved" version?

I have one of the originals from Tony and always thought it was right on....perhaps not.

George

PS. Ty, if ANY engine should work with a Vibratach, it should have been the Fox. Don't remember them as being accurate but I remember the model mag advertisements in the fifties, and even SAW one back then. 

I have an LCD display mini-tach.  Works fine except when exposed to direct sunlight for an extended period.  The display blanks out black.  It's a characteristic of all LCD displays, my stopwatches do the same thing.  The display just needs to cool down, then will work normally.

Hi ,

I may as well throw my two cents worth  in , about now .
I have a Glo-Bee tach and it has somewhat of an extreme variance in readings .
When I was breaking in my Ro-Jett .40 , the tach would jump from 10.5K to 13.8K , even when the tach was mounted in a secure location , to prevent it from being inadvertently moved . The air temp was only in the mid seventies and it had a fresh nine volt battery .
My ears are good (so my girlfriend says) so I think I would hear the increase in RPM's

I really appreciate the help 

Rob Killick

I believe some countries use 50 cycles, so I guess it would read 3,000 rpm there?

Yes, for Australia 3,000 is the correct reading for flouro lights. I had a Thunder Tiger tach that started giving much higher readings than it should have and the flourescent light check confirmed this. I threw it away, Thunder Tiger tachos need to be almost in the prop to actually read the RPM, a fact I found very annoying. My latest tacho is a Taiwanese Lutron DT-602 which has a lense and hood and can read a spinning prop from a mile away. Unfortunately it also reads flourescent lights at 2,900    , dammit. I might just buy another tacho to get comparisons. I also own a Vibra-tach but I'm not gonna bother with it, keepsake only.

As Floyd mentioned, calibrating at line current frequency only means the reading is correct at THAT freq/RPM, but it is a start...

Most of the available tachs I've seen CAN be opened (Haven't had a close look at that red one, though.) There are trim pots somewhere on the circuit board. They can be calibrated on a fresh battery with the case open, but there may the reading may shift when the box is closed back up. Watch for that and accommodate it.

I've heard that LCD screens are sensitive to direct sunlight; hadn't heard about high temperature affecting them. Thanks!

As to direct sunlight, I even turn my Casio LCD wrist watch under my wrist when driving, or out in bright Arizona sun for extended time. It's now about 4 years old, and been through a few battery replacements, but still has a clean, bright display... Hasn't burned black yet, either...

Still have a Vibra-Tak from the 1950's, and the collet is still nice and tight. Never did stick the pin through a prop - yet, anyway. It did "work" as consistently as the operator let it, and in the 1950's there were no electronic alternatives. There WERE revolution counters, where you pushed a padded shaft end onto the spinner or prop nut and timed the count to get the RPM (RPM = counter reading X 4 for a 15 second timing, e.g.). Never interested in THAT...