AzBilliards.com Easy way to measure an angle in degrees
 Page 4 of 4 « First < 234
 (#46) AimPro Billiards Registered   Status: Offline Posts: 6 vCash: 500 iTrader: 0 / 0% Join Date: Aug 2020 08-05-2020, 04:54 PM yes, you are right. I see that now. My mistake. Thanks for the explanation.

(#47)
Bob Jewett
AZB Osmium Member

Status: Offline
Posts: 18,505
vCash: 1700
Join Date: Apr 2004
Location: Berkeley, CA

08-05-2020, 05:39 PM

Quote:
 Originally Posted by AimPro Billiards yes, you are right. I see that now. My mistake. Thanks for the explanation.
BTW, I used to take the perpendicular as in your calculation but many years ago someone (here? RSB?) pointed out that the base of the isosceles triangle has less error -- and is easier to use on the table.

Bob Jewett

 (#48) AimPro Billiards Registered   Status: Offline Posts: 6 vCash: 500 iTrader: 0 / 0% Join Date: Aug 2020 08-05-2020, 06:24 PM I'm embarrassed to remember that I learned how to do this exact problem correctly in high school math -- and apparently forgot! I also forgot the basic approach of drawing a diagram before writing any equations, thinking it was too simple a problem to need that. But I'm intrigued by your comment that the correct method is easier to do on the table. Could you explain that. To me, it's just estimating the distance between the two endpoints. [Put finger down to mark starting position; move cue to other position and estimate the distance.] You are suggesting to estimate half the distance and doubling it is somehow easier as well as more accurate?
(#49)
Bob Jewett
AZB Osmium Member

Status: Offline
Posts: 18,505
vCash: 1700
Join Date: Apr 2004
Location: Berkeley, CA

08-06-2020, 01:13 PM

Quote:
 Originally Posted by AimPro Billiards ... You are suggesting to estimate half the distance and doubling it is somehow easier as well as more accurate?
No. The division into two separate distances is only in the analysis. The measurement is of the base of an equilateral triangle for which the two sides are your cue stick. Just like in the original diagram. Only the entire distance is measured. From the position of the bumper to the new position of the bumper. That distance is the number of degrees directly. No division or multiplication. Just take the distance.

(For angles over 45 degrees, you measure the complement and subtract, as described above. But that is only for such thin cuts.)

Bob Jewett

 (#50) AimPro Billiards Registered   Status: Offline Posts: 6 vCash: 500 iTrader: 0 / 0% Join Date: Aug 2020 Yesterday, 08:08 AM OK, thanks. I get it. I'll comment that in the past, I've tried measuring the complement angle for thin cuts. It's the obvious approach. But it didn't work for me generally, because I found that estimating the line of the complement (the tangent) was not easy for me to do accurately enough (within one degree). Do you have any suggestions of an easy way to get the tangent direction accurately? My only method is using "Table Geometry" (see my video https://www.youtube.com/watch?v=4PGSQiq5b9g&t=186s) and getting the "Object ball angle", to which I can add 90 degrees. But at that point, I'd rather just get the "Cue ball angle" and compute the cut angle.
(#51)
Bob Jewett
AZB Osmium Member

Status: Offline
Posts: 18,505
vCash: 1700
Join Date: Apr 2004
Location: Berkeley, CA

Yesterday, 11:15 AM

Quote:
 Originally Posted by AimPro Billiards O ... Do you have any suggestions of an easy way to get the tangent direction accurately? ...
The best I know of, other than to use a fixture is to place my cue stick as in response 28.

Bob Jewett

 Dr. Dave and Bob J to the rescue
(#52)
Imac007
AzB Silver Member

Status: Offline
Posts: 301
vCash: 500
Blog Entries: 1
Join Date: Dec 2017

Dr. Dave and Bob J to the rescue - Yesterday, 10:52 PM

Quote:
 Originally Posted by AimPro Billiards OK, thanks. I get it. I'll comment that in the past, I've tried measuring the complement angle for thin cuts. It's the obvious approach. But it didn't work for me generally, because I found that estimating the line of the complement (the tangent) was not easy for me to do accurately enough (within one degree). Do you have any suggestions of an easy way to get the tangent direction accurately? My only method is using "Table Geometry" (see my video https://www.youtube.com/watch?v=4PGSQiq5b9g&t=186s) and getting the "Object ball angle", to which I can add 90 degrees. But at that point, I'd rather just get the "Cue ball angle" and compute the cut angle.
One comment stuck in my mind. It had to do with why would a player want to know an angle to pocket a ball? None of the aiming systems I know are based on a way to target based on degrees. But there is one area of the game where knowing the angle is beneficial, position. The benefit of knowing the cb path in degrees after contact tells us how to avoid scratches, whether the cb will miss or hit a ball off contact or If the path into a rail will result in position.

“Rolling Cue Ball Deflection Angle Approximations” ILLUSTRATED PRINCIPLES David Alciatore, PhD (“Dr. Dave”) https://billiards.colostate.edu/bd_a...2011/nov11.pdf is a great place to start. While Dr. Dave’s peace sign can be used from the cue ball side of the collision to estimate where the rolling ball will deflect after contact, the fact that it is known to approximate 30° can be used from the opposite side of the shot. Line the ghost ball centre to the cb centre with the cue. My shaft on my cue is 29 inches. Pivoting my cue joint, from the gb centre through ~15 inches equals about 30°. That applies on the ¼ through ¾ ball cuts. On thinner cuts the formula used is about 70% of the angle from cue line to tangent line. This allows a player at the table to simply use the cue to find the natural rolling path off contact on these thin shots.

(#53)
Patrick Johnson
Fish of the Day

Status: Offline
Posts: 21,772
vCash: 1700
Join Date: Jun 2007

Yesterday, 10:58 PM

Quote:
 Originally Posted by Imac007 Pivoting my cue joint, from the gb centre through ~15 inches equals about 30°.
This is equivalent to Bob’s technique of moving the butt 30 inches.

pj
chgo

(#54)
Imac007
AzB Silver Member

Status: Offline
Posts: 301
vCash: 500
Blog Entries: 1
Join Date: Dec 2017

Today, 12:28 PM

Quote:
 Originally Posted by Patrick Johnson This is equivalent to Bob’s technique of moving the butt 30 inches. pj chgo
Exactly the point of the perceptual move to the joint, especially when the surroundings make it easier. The cue can be used at the table to measure both 58” and half that amount 29”. Thinking inside the box, working with what’s there.

Paths into a rail also remain the same regardless of which end you look at them. A good example, I teach, has to do with spot on the wall. The concept is explained here. https://billiards.colostate.edu/bd_a...2011/feb11.pdf

It can be combined with another concept called Magic Spot. The 3 cushion diagram 1 in the Dr. Dave spot on the wall pdf goes over the spot, for that table. The idea is explained here. https://billiards.colostate.edu/reso...image_kick.pdf

Once the mirror contact point is decided, the line from the starting point through the magic spot tracks to the mirror. Of course, the cb is seldom in the reflective position at the table. By extending the original cue line, as in the spot on the wall idea, a new spot on the wall is established.

But there is almost never a convenient wall. The trick is for the player to become the spot. From the spot, the player can pivot to the cb location. Where that line crosses the rail becomes the new cue line. The point is the line crosses the rail at the same location regardless of which end of the line you look from.

Sometimes you need to calibrate for the magic spot. Tables are different. The method is quite simple. Starting from the corner, discover the line to the first rail that ends up, using running side, as 3 to the corner (the mirror). Once that track is known the trick is to find another mirror track to the third cushion. A good place to begin is from the second diamond up the long rail from the original corner start. Pick a starting point on the rail. The contact point on the opposite rail off 3 cushions through the magic spot with running follow should mirror the starting position. For the table you are calibrating, the magic spot must lie somewhere along that line or the table won’t work.

Where the two mirror image shot lines cross is the calibrated magic spot for the table.

 Page 4 of 4 « First < 234

 Thread Tools Rate This Thread Rate This Thread: 5 : Excellent 4 : Good 3 : Average 2 : Bad 1 : Terrible

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Main Category     Main Forum     Live Stream Area     Wanted/For Sale         For Sale Items         eBay Auctions         Wanted     Room Owner Discussion     14.1 Pool     Canadian Pool     Snooker     Carom Billiards     Memories of Steve Mizerak     English Pool     Billiard and Pool History in the U.S.     BEF Juniors Pool     Test Area     Cuesports: Rules & Strategies     AzB Hall of Fame     Pool Room Reviews Tournament Talk     U.S. Tournament Announcements     European Tournament Annoucements     Asian Tournament Announcements     Super Billiards Expo     Junior National 9-Ball Championships     World Championships     US Open Championships     Derby City Classic/Southern Classic     BCA Pool League World Championships     US Bar Table Championship     WPBA     Matchroom Events     Eurotour     Other Tours & Events Products Talk     Pool Tables and Accessories Reviews     Cue Reviews     Cue and shaft reviews     Cue Case Reviews     Cue Machinery and Supplies     Cue & Case Gallery     Ask The Cuemaker     Cue Accessory reviews     Other Item reviews     Talk To A Mechanic Instruction & Ask the pros     Aiming Conversation     George 'Ginky' San Souci     Instructional Material reviews     Instructor Reviews     Melissa Morris     Sarah Rousey     Ask The Instructor