Victorian Numeral 2c Purple/Violet Differences

Purchased these online, they are all MNH, described as Sg153, Sg154 and Sg154a ( from left to right)and I'm trying to establish what they are equal to in the Unitrade catalogue.
76, 76a, 76i or 76ii
The left hand stamp seems thicker than the others, I use the word seems that's because it's by feel, but not 100% sure…how do you measure paper thickness accurately.
Apart from shade difference the two right hand ones look the same. Although according to Sg catalogue 154a is supposed to be reddish purple….has anyone got a reddish purple equivalent to show me in this forum to see if it matches mine, according to Unitrade this should be 76ii
All help appreciated

With a micrometer, or a paper guage.
Micrometers are about $25 second hand.
One has to be VERY faint in screwing the anvils together.
The faintest touch on the knurled end, when the anvil stops
and your fingers slip, read the measurments in 1000th of an inch.

When you rub your index finger and thumb together, when barely feeling it, that is the pressure on the knurled end.

All stamps have to be the same, ie with or without gum.

Here you go - 76 first and 76ii next. With usual caveat on shades appearing different based on scanners/monitors used.

~Greg

Many thanks….your reddish purple looks more like it….I don,t think any of mine are anything like that…
Thanks for response

Just to add there can be some variation in the reddish purple - see the strip below where the shading differs from left to right.

Personally I wouldn't call your rightmost stamp reddish purple. Hope that helps.