convert num(fieldname) as depth does not convert field to a number

[tzitello_splunk]

When I run the following search, the field does not convert to a number:
search| convert num(Samples.Sample.Depth) as depth

depth field shows up as alpha numeric instead of numeric (a instead of #)
I am running V 7.2.1

[woodcock]

Don't worry about that; what does this show when you add it?

| eval type=typeof(depth)

Also, is the value on the Statistics tab right-justified ( string ) or left-justified ( number )?

[whrg]

Could you give an example?