Trick to flipping axis

**mshimp** · 10-11-2014, 09:03 PM

When we transpose a prescription we have been taught to change the axis by 90 degrees. 1-90 add 90 degrees, more than 90 subtract 90 degrees. Years ago learning to calculate a slab off or trouble shooting an rx with a patient, I needed to be able look at an rx in both power meridians and where the axis would be, and to do it quickly. I discovered that you could flip a three digit axis instantly by adding one to the middle number and dropping the one in front. On two digit numbers its just the opposite. Subtract 1 from the first, or tens unit, then add 1 to the hundreds unit. With two digit numbers it does not work with the 91 to 99 degrees. Just subtract 90 degrees from them. Sometimes it sounds more complicated, but its not. For me its fast without thinking. Have fun!

**mshimp** · 10-11-2014, 09:11 PM

Numbers 1- 9 just add 90!

**HarryChiling** · 10-12-2014, 06:51 PM

You could just add 90 to all and if they're over 180, subtract 180.

The opposite holds true as well subtract 90 from all, if they're negative add 180.

When programing one of the above methods is preferable, I subtract because it's easier to check for two cases if >= 0 add 180.

**mshimp** · 10-12-2014, 07:12 PM

After awhile there is no adding or subtracting. You just look at it and you know instantly. Example 115 is 25 no thinking. 75 is 165 no thinking and so on.

**Uilleann** · 10-13-2014, 09:25 AM

This sounds a bit like figuring out / remembering which runway to land on when the wind changes. :)

**pseudonym** · 10-13-2014, 09:51 AM

It's easier. Mike DiSanto used to show this method in his ABO reviews. For a while, I did it this way then checked it on the calculator. Works everytime. Except for the 91-99 you mentioned but that's where going back to "subtract 90" or 1-9 "add 90" just seems natural. Plus it's freeing not to have to fumble for a calculator every time you have to do a transposition.