Full disclosure: I am not an actual surveyor. Today I went to a local set of NOAA markers to check my 100' handyman-type steel tape. It was near the small Aurora OR airport. They have some marks set out for checking such a length, that are stated as 99.99 feet apart, according to removed link and one description there is "THE 0-METER POINT IS A 3 INCH PLAIN BRASS DISK STAMPED "P.L.S.O. STA. NO. 1 0+00 TEST BASE 1973"
SET IN THE TOP OF A 30 CM (12 IN) DIAMETER CONCRETE POST FLUSH WITH THE SURFACE OF THE GROUND."
As a new user apparently I can't post photos but my question was about the appearance of that particular marker disk. I found it set in the concrete post, reasonably smooth, stamped as described, and there is the X mark in the middle, all as expected. However, there are also probably 25 or more distinct, small hemispherical dimples or pock-marks of various size up to maybe 2 mm in diameter, randomly scattered across the entire face area. I am curious, is this typical for such markers? Some kind of corrosion process maybe, since 1973? But these holes do not have a different color than the rest of the metal, and they are mostly very round, as if stamped or carved out by a tool.
I’m a Portland area surveyor and am familiar with that monument. It was damaged like that the first time I saw it in the mid 1990’s. Use the cross.
There are 2 other baselines in the PDX area but neither have a 100 foot mark for checking chains. That one is a relic of a bygone era.
Thank you for your reply, I appreciate it!
FWIW I found my tape when pulled reasonably taut reached the 100 ft (well, 99.99) mark as nearly as I could read it- at least on this sunny 74 F day. That is better than I expected for the cheapest 30 m / 100' steel tape that Amazon sells.
I'm glad the old relic is still there. Without access to any of the modern tools of the surveying trade, I don't know where else I could have checked that length.
BTW - your steel tape will lengthen in warm summer weather and contract as the weather cools. Also, the amount of tension you apply will affect the measurement. There are equations to calculate the effect. Your handyman-type tape probably hasn't been standardized like a surveyor tape would be, but the effect is still there. I wouldn't be surprised if you read, in August, maybe 99.96' between the standard 99.99' marks. There probably isn't anything wrong with your tape. It's just warm.
I have used that baseline myself back in the mid 90’s. If memory serves me correctly the edm portion of that baseline moves a bit over time.
To the OP. On your tape there is usually a small area if you are like me a magnify glass will be required or maybe in the instructions. Anyway a coefficient for a specific temperature if still or iron clad it’s usually at 68 degrees F. Above or below that temp at the correct tension is how one would compute the actual distance vs read distance based on temperature. There are swag the dip over the span correction tension etc. I still have a couple tension gauges.glad to see someone check their equipment out.
Shooting from the hip, I believe that expansion coefficient is 0.00000645' x (current temp-68F). Add or subtract(depending on which side of 68F you are) that number from you measured distance. I've forgotten a lot of things since school but that one always stuck. Probably because throwing chain was the very first thing we learned!I have used that baseline myself back in the mid 90’s. If memory serves me correctly the edm portion of that baseline moves a bit over time.
To the OP. On your tape there is usually a small area if you are like me a magnify glass will be required or maybe in the instructions. Anyway a coefficient for a specific temperature if still or iron clad it’s usually at 68 degrees F. Above or below that temp at the correct tension is how one would compute the actual distance vs read distance based on temperature. There are swag the dip over the span correction tension etc. I still have a couple tension gauges.glad to see someone check their equipment out.
@jflamm funny how some things just stick in your head. For some reason I want to say around 10 degrees plus or minus 68 it’s like about .02’ per hundred feet as a rule of thumb for the old yellow steel tapes. But man that was in the 90’s where all that was in my pea brain.
@olemanriver No doubt! That one's been hanging in there since fall of 97.