what formula should I use?

[Optometry student]

Can anyone please help me with this question?

A lens measure scaled for glass of refractive index 1.654 is placed upon a brass tube and the instrument is rotated until the legs lie at right angles to the axis of the tube. The reading given by the instrument in this position is +10.50, what is the external diameter of the tube in cm?

[Wes]

65.4/10.5 *2

[PhiTrace]

Divide the above respose by 100 to get the measure in centimeters.

[Wes]

The formula I provided gives the answer im cm. If you divide it by 100, you will have the answer im meters. The poster asked for a formula that would result in cm, so I provided it.

[Optometry student]

got it. I misunderstood the question. that's why couldn't get the answer. thanks so much.

[fjpod]

Glad to see they are still teaching useful applications with the lens clock in optometry school. Normal people would just take a ruler and measure it.

[Dion]

Divide the above respose by 100 to get the measure in centimeters.

Yes i totally agreed with you and I'm also using this formula to calculate the diameter. Thanks and i hope in future you also updated us.