Is using an ankle for the blood pressure cuff accurate?

I doubt it. Especially on the ankle, because they are very different physically. The leg analog of the upper arm should be your thigh or maybe calf, not your ankle.

A possible test: If you have a BP device, try it on your arm followed by your ankle (multiple times because they tend to vary with each reading, so then take the average results), and see if the averages agree at all between arm and ankle (or a more sensible place on your leg).

No. For the most accurate readings, they always use the left arm.

I learn left upper arm or left wrist.

I think so. When I worked with animals, we used mainly the front limbs. But we used rear legs too, and sometimes the tail.

On smaller reptiles, we used a doppler system, in which we placed a special diode on the base of the underside of the tail. Essentially, we check BP, by occludining an artery…

I’m going to base my answer on simple hydraulics and physics – not actual testing. .
A blood pressure reading is supposed to be taken with the cuff at the level of the heart. If you are flat on a table with the cuff at the level of your heart the reading should be close. But if you take your BP while sitting, your readings will be off. If the cuff is higher than your heart you can expect to see lower values, If the cuff is below your heart you can expect to see higher numbers. How much is this effect? Let’s use some physics!

The readings are in units of mm of Hg. say you have a typical BP of 120/80.
If we assume blood has a density similar to water we can calculate the effect of height by converting the pressure head of a column of water of the same height.
Let’s raise your arm 1 ft, 30 cm, above your heart. ..... I made a spread sheet that converts inches of water, to inches of Hg, then converted that to mm of Hg. The calculation added that value to the base number of 120/80. So… You can expect to see a change of 22mm Hg per foot of height difference above or below your heart.
If your reading is 120/80 at the level of your heart, I predict it will read 98/58 if your arm is raised up one foot. Conversely if your arm is suspended below your heart the reading would be higher 142/102. If your arm or ankle is 2 ft below your heart you can expect to see a reading of 165/125.

Now we need someone to experiment and verify my numbers. It is an easy experiment. Take your BP at the recommended position and repeat the test with your arm or leg in various postions above and below your heart. Any volunteers?

^I actually have a BP monitor. I just can’t find it. I may have lost it in one of my previous floods. If I find it, I’ll see if I can try some experimentation. I only have/had one cuff/size though, do I’ll have to see if it fits more than my arm size, from 7 years ago…

I’m pretty curious about the results, and I will update, if I can find the monitor.

What @LuckyGuy said.